As 4678-2002 Earth-Retaining Structures

AS 4678—2002 (Incorporating Amendment No. 1)

Australian Standard™

Earth-retaining structures

AS

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This Australian Standard was prepared by Committee CE-032, Reinforced Soils and Retaining Structures. It was approved on behalf of the Council of Standards Australia on 16 November 2001 and published on 26 February 2002.

The following are represented on Committee CE-032:

Association of Consulting Engineers, Australia

Australian Industry Group

Australian Geomechanics Society

AUSTROADS

Cement and Concrete Association of Australia

Concrete Institute of Australia

Concrete Masonry Association of Australia

Construction Industry Advisory Council

Institution of Engineers, Australia

Master Builders Australia

University of New South Wales

University of Technology, Sydney

Keeping Standards up-to-date

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Detailed information about Standards can be found by visiting the Standards Australia web site at www.standards.com.au and looking up the relevant Standard in the on-line catalogue.

Alternatively, the printed Catalogue provides information current at 1 January each year, and the monthly magazine, The Global Standard, has a full listing of revisions and amendments published each month.

We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at [email protected], or write to the Chief Executive, Standards Australia International Ltd, GPO Box 5420, Sydney, NSW 2001.

This Standard was issued in draft form for comment as DR 96405.

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http://www.standards.com.au

AS 4678—2002 (Incorporating Amendment No. 1)

Australian Standard™


First published as AS 4678—2002. Reissued incorporating Amendment No. 1 (July 2003).

COPYRIGHT

© Standards Australia International

All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher.

Published by Standards Australia International Ltd GPO Box 5420, Sydney, NSW 2001, Australia

ISBN 0 7337 4238 6

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PREFACE

This Standard was prepared by the Standards Australia Committee, CE-032, Reinforced

Soils and Retaining Structures, in response to a call from the building industry for the

establishment of a Standard on earth-retaining systems, including reinforced soils.

This Standard incorporates Amendment No. 1 (July 2003). The changes required by the

Amendment are indicated in the text by a marginal bar and amendment number against the

clause, note, table, figure or part thereof affected.

The objective of this Standard is to provide designers of earth-retaining structures with

design criteria and guidance for use in design applications.

The terms ‘informative’ has been used in this Standard to define the application of the

appendix to which it applies. An ‘informative’ appendix is only for information and

guidance.

As far as practicable, this Standard has been made consistent with the approach taken in the

loading code for structures, AS 1170, Minimum design loads on structures. This enables the

Standard to be used in combination with structure design Standards such as AS 1720,

Timber Structures, AS 3600, Concrete Structures, AS 4100, Steel Structures, and AS 3700,

Masonry structures. Some specific applications are covered by other Standards and

documents. For example, HB77, Australian Bridge Design Code, should be used to design

earth-retaining structures associated with road bridges.

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CONTENTS

Page

SECTION 1 SCOPE AND GENERAL

1.1 SCOPE......................................................................................................................... 5

1.2 APPLICATION ........................................................................................................... 6

1.3 REFERENCED DOCUMENTS................................................................................... 7

1.4 DEFINITIONS............................................................................................................. 7

1.5 NOTATION............................................................................................................... 11

SECTION 2 INVESTIGATION AND TESTING

2.1 INVESTIGATIONS................................................................................................... 15

2.2 TESTING................................................................................................................... 17

SECTION 3 DESIGN REQUIREMENTS

3.1 GENERAL................................................................................................................. 18

3.2 DESIGN CONSIDERATIONS FOR ULTIMATE LIMIT STATE............................ 18

3.3 DESIGN CONSIDERATIONS FOR SERVICEABILITY LIMIT STATE................ 19

3.4 DESIGN LIFE ........................................................................................................... 27

3.5 DURABILITY AND PERFORMANCE OVER TIME .............................................. 28

3.6 DRAINAGE .............................................................................................................. 28

3.7 INFLUENCE OF CONSTRUCTION ON ADJACENT GROUND AND

STRUCTURES.......................................................................................................... 29

3.8 SUBMERGED STRUCTURES ................................................................................. 29

3.9 CONNECTIONS ....................................................................................................... 30

SECTION 4 DESIGN LOADS

4.1 LOADS...................................................................................................................... 31

4.2 LOAD COMBINATIONS ......................................................................................... 31

SECTION 5 MATERIAL DESIGN FACTORS

5.1 GENERAL................................................................................................................. 33

5.2 MATERIAL STRENGTH FACTORS FOR SOIL SHEAR STRENGTH.................. 33

5.3 MATERIAL FACTORS FOR STRUCTURAL COMPONENTS .............................. 34

5.4 STRUCTURE CLASSIFICATION FACTOR ........................................................... 34

5.5 STRENGTH FACTORS FOR SOIL REINFORCEMENT ........................................ 35

SECTION 6 CONSTRUCTION

6.1 GENERAL................................................................................................................. 39

6.2 CONSTRUCTION TOLERANCES........................................................................... 39

6.3 SPECIFIC REQUIREMENTS ................................................................................... 40

SECTION 7 PERFORMANCE MONITORING .................................................................... 42

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Page

APPENDICES

A STRUCTURE CLASSIFICATION............................................................................ 43

B GROUND ANCHORS............................................................................................... 46

C SOIL NAILING FOR EARTH-RETAINING STRUCTURES .................................. 54

D SOIL AND MATERIAL PROPERTIES.................................................................... 60

E DESIGN MODELS AND METHODS....................................................................... 69

F MATERIAL SELECTION AND DURABILITY....................................................... 76

G DRAINAGE OF EARTH-RETAINING STRUCTURES .......................................... 79

H REINFORCED SOIL FACING SYSTEM CONNECTION LOADS ......................... 90

I EARTHQUAKE DESIGN ......................................................................................... 92

J LOAD COMBINATIONS ....................................................................................... 103

K PARTIAL MATERIAL STRENGTH FACTOR DETERMINATION FOR SOIL

REINFORCEMENT ................................................................................................ 118

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STANDARDS AUSTRALIA

Australian Standard


S E C T I O N 1 S C O P E A N D G E N E R A L

1.1 SCOPE

This Standard sets out requirements and recommendations relating to the design and

construction of structures required to retain soil, rock and other materials. It also includes

requirements and recommendations for the reinforcement of soil and rock materials.

This Standard does not prescribe specific methods of analysis.

NOTE: Various organizations and authorities may develop detailed guides and specifications

based on the principles set out in this Standard.

This Standard is in limit state format.

This Standard does not provide requirements and recommendations for ‘revetment type’

structures, which are sometimes used to retain soil, rock and other materials at slopes

steeper than that which the soil, rock or other material would naturally assume.

The retaining structures encompassed by this Standard are indicated in Figure 1.1.

Facings constructed up to 800 mm high in a Type 3 structure application are not covered by

this Standard.

FIGURE 1.1 RETAINING AND REVETMENT STRUCTURES

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FIGURE 1.2 TERRACED STRUCTURES

1.2 APPLICATION

1.2.1 General

This Standard is applicable to retaining structures and reinforced soil structures that are

commonly constructed for engineering works and infrastructure. Such structures are

typically up to 15 m in height.

Structures of unusual shape, of large retained heights (in excess of 15 m) or founded in

unusual ground conditions (such as soft ground, land slips, steep sides or deeply inclined

gullies), together with structures subject to sustained cyclic loading, are outside the

provisions of this Standard.

This Standard does not apply to the design and construction of water-retaining structures

(such as dams and reservoirs) or bridge structures.

1.2.2 Structure classification

Structures shall be classified in accordance with Table 1.1.

NOTE: ‘Not applicable’

TABLE 1.1

STRUCTURE CLASSIFICATION

Classification Examples of structures

C Where failure would result in significant damage or risk to life

B Where failure would result in moderate damage and loss of services

A Where failure would result in minimal damage and loss of access

NOTES:

1 Classification B includes structures not covered by Classifications A or C.

2 For more information on structure classification, see Appendix A.

Structures where failure would result in minimal damage and loss of access where the wall

height (H) is greater than 1.5 m are deemed to be classification B structures.

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1.3 REFERENCED DOCUMENTS

The following documents are referred to in this Standard:

AS 1170 Minimum design loads on structures (known as SAA Loading Code)

1170.1 Part 1: Dead and live loads and load combinations

1170.2 Part 2: Wind loads

1170.4 Part 4: Earthquake loads

1726 Geotechnical site investigations

1289 Methods of testing soils for engineering purposes

1289.6.3 Method 3: Determination of the penetration resistance of a soil

1720 Timber Structures (all parts)

2159 Piling—Design and installation

2439 Perforated plastics drainage and effluent pipe and fittings (all parts)

2870 Residential slabs and footings

2870.1 Part 1: Construction

3500 National Plumbing and Drainage Code (set)

3600 Concrete structures

3700 Masonry structures

4100 Steel structures

SAI

HB77 Australian Bridge Design Code

BS

8006 Code of practice for strengthened/reinforced soils and other fills

1.4 DEFINITIONS

For the purpose of this Standard, the definitions below apply.

1.4.1 General

1.4.1.1 Action

A cause of stress, dimensional change, or displacement in a structure or component of a

structure.

1.4.1.2 Action effect

The internal force, moment, deformation, crack, or the like effect caused by one or more

actions.

1.4.1.3 Batter

A slope of a cut or fill.

1.4.1.4 Characteristic value

Representative value of a soil, rock or a material property.

NOTE: For soil properties, the characteristic value is a cautious estimate, that is, close to but not

greater than, of the mean value, (see Clause 5.2.3). The strengths of materials, such as concrete,

steel, plastic and masonry, are contained in the appropriate Standards.

1.4.1.5 Dead load

The load determined in accordance with this Standard imposed by the components of the

self-weight of the structure and retained soil or rock.

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1.4.1.6 Design life

The intended period of time over which the structure is required to fulfil its function and

remain in a serviceable state.

1.4.1.7 Design load (action)

The appropriate combination of loads (actions) and load factors as specified in this

Standard.

1.4.1.8 Ground anchor

A tensile reinforcement, wire or bar, and its associated components that transmit force into

soil or rock through bond over part of its length.

NOTE: Appendix B gives guidance on design of ground anchors.

1.4.1.9 Limit state

Any limiting condition for which structures are designed.

NOTE: The limit states design criteria considered in this Standard are strength limit state,

stability limit state and serviceability limit state.

1.4.1.10 Live load

The load as defined in this Standard assumed to arise from the intended use of the structure

including distributed, concentrated, impact and inertia loads, but excluding wind, snow, and

earthquake loads.

1.4.1.11 Load factor

A factor specified in this Standard for structural design to be used with the loads (or

actions) in deriving design loads (or design actions).

1.4.1.12 Resistance effect

The characteristic strength multiplied by the appropriate reduction factors for ultimate or

serviceability limit state analysis.

1.4.1.13 Rock bolt

A tensile reinforcement, typically a bar of 15 to 50 mm in diameter, of steel or high strength

polymer, which is inserted into a drill hole in rock and fixed in position by grout or

mechanical anchorage.

NOTE: An initial tension is applied equal to or greater than 5%, and usually about 50% to 60%,

of the ultimate tensile strength of the bar.

1.4.1.14 Rock dowel

As for rock bolt except that the applied tension is less than 5% of the ultimate tensile

strength of the material used in the bar.

1.4.1.15 Serviceability limit state

A limit state for acceptable in-service conditions.

1.4.1.16 Stressed ground anchor

A tensile reinforcement, typically high tensile steel strand or wire or bar, and its associated

components that transmit force into soil or rock through bond over part of its length. An

initial tension is applied and the minimum capacity is usually checked by proof loading.

1.4.1.17 Soil dowel

A relatively stiff structural element used to take load in soils principally by shear action.

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1.4.1.18 Soil nail

A tensile reinforcement, typically a steel bar or high strength polymer bar, placed in the

ground and bonded for all or a majority of its full embedded length.

NOTE: Soil nails normally have no applied or nominal initial tension and mobilize axial force by

relative movement with the soil. For more information on soil nailing for earth-retaining

structures, see Appendix C.

1.4.1.19 Strength limit state

A limit state of collapse or loss of structural integrity.

1.4.1.20 Stability limit state

A limit state corresponding to the loss of static equilibrium of a structure or part of

structure considered as a rigid body.

1.4.1.21 Sprayed concrete

A mixture of cement, aggregate and water (it may also include fibres and/or cement

mixtures), conveyed through a hose, and projected at high velocity from a nozzle into place,

to produce a dense homogeneous mass and may be applied by either a dry-mix, or a wet

mix process.

1.4.1.22 Facing

Unit for erosion protection or aesthetic purposes constructed in front of an otherwise stable

slope.

NOTE: The facing may or may not include drainage consideration.

1.4.1.23 Stable slope angle (i)

The angle that the soil, rock or other material would naturally assume in the long term

under the expected variety of external (e.g., environmental), and internal (e.g., seepage)

conditions.

1.4.1.24 Wall height

The overall height between the top and the toe of the wall where the line between the points

is sloped equal to or greater than 70 degrees from the horizontal.

1.4.1.25 Wall height for terraces

The overall wall height for terraces is the height between the top of the top wall and the

bottom of the bottom wall, except where the terraces are spaced sufficiently far apart

horizontally so that the equivalent average slope of the terraced wall thus formed is below

the stable slope angle, i (see Figure 1.2). In such cases the walls are considered separately.

1.4.2 Geosynthetic materials

1.4.2.1 Geocomposite

A composite geosynthetic material made up from geotextiles, geogrid and related products,

as appropriate, to form a composite geosynthetic material.

1.4.2.2 Geogrid

A planar structure consisting of elements in an open grid pattern, used for ground

reinforcement.

1.4.2.3 Geosynthetic reinforcement

A generic term that encompasses flexible synthetic materials used in geotechnical

engineering, such as geogrids and geotextiles.

1.4.2.4 Geosynthetic subsurface drainage system

A pervious subsurface drainage system prefabricated from synthetic materials.

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1.4.2.5 Geotextile

A permeable, polymeric material which may be woven, non-woven or knitted.

1.4.3 Soil and rock materials

1.4.3.1 Cohesive fill

Naturally occurring or processed materials with greater than 50% passing the 75 µm

AS sieve and a plasticity index of less than 30% and liquid limit of less than 45%.

1.4.3.2 Controlled fill—Class I

Soil rock or other inert material that has been placed at a site in a controlled fashion and

under appropriate supervision to ensure the resultant material is consistent in character,

placed and compacted to an average density equivalent to 98% (and no test result below

95%) of the maximum dry density (standard compactive effort) for the material when tested

in accordance with AS 1289.5.1.1.

NOTE: For cohesionless soils, material compacted to at least 75% Density Index is satisfactory.

1.4.3.3 Controlled fill—Class II

Soil rock or other inert material that has been placed at a site in specified layers in

controlled fashion to ensure that the resultant material is consistent in character placed and

compacted to an average density equivalent to 95% (and no test result below 92%) of the

maximum dry density (standard compactive effort) for the material when tested in

accordance with AS 1289.5.1.1.

NOTE: For cohesionless soils, material compacted to at least 65% Density Index is satisfactory.

Generally the layer thickness is specified as a maximum of 300 mm.

1.4.3.4 In situ material

Natural soil, weathered rock and rock materials.

1.4.3.5 Other fill

Materials that are chemically unstable or physically decomposable, which may include blast

furnace slag, fly ash and topsoil.

1.4.3.6 Reinforced soil

The material in a reinforced soil structure in which reinforcing elements are installed to act

through interface friction, or other means, to improve the stability of the soil or rock

materials.

1.4.3.7 Reinforced soil structure (RSS)

A structure formed by reinforced soil, facing materials, drainage and associated foundation

systems.

1.4.3.8 Retained backfill

The fill material located behind a retaining structure.

1.4.3.9 Select fill

A soil, rock or other inert material that is selected from various materials, that may be

available on a site, and that has particular properties specified by a designer.

NOTE: Select fill will also generally be a soil or rock material that does not include highly plastic

clays, topsoil, large boulders or waste products.

1.4.3.10 Uncontrolled fill

Soil, rock or other inert material that has been placed at a site and that does not fall under

the definitions for materials in Clauses 1.4.3.2 and 1.4.3.3.

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1.4.4 Drainage

1.4.4.1 Piped drains

A system of impervious pipes designed to lead drainage away from the retaining structure.

1.4.4.2 Subsoil drain

A system of pervious subsurface pipes, which is used in soil materials to collect ground

water.

1.4.4.3 Subsurface drainage system

A system of drainage measures designed to remove water and seepage from the ground,

which may include all, or a combination of, pervious granular materials, geocomposite,

subsoil drains and piped drains.

1.4.4.4 Vertical structure drain

A vertical drainage system located behind and adjacent to a retaining wall, reinforced soil

structure or its facing, comprising a pervious medium for the dewatering of the retained soil

mass.

1.5 NOTATION

The following symbols are used in this Standard:

Ac = corrosion loss at t = 1 year

Ao = original cross-section area

a = acceleration coefficient derived in accordance with AS 1170.4

ah = horizontal coefficient of acceleration (pseudo-static)

‘Not applicable’

am = maximum wall acceleration coefficient at centroid

amh = average amplified horizontal acceleration coefficient

amv = average amplified vertical acceleration coefficient

av = vertical coefficient of acceleration (pseudo-static)

B = base width

c = characteristic cohesion of a soil, which is a parameter in the Mohr-Coulomb

failure law, also referred to as the cohesion intercept

c′ = characteristic effective cohesion of a soil

cu = characteristic undrained cohesion of a soil

c* = design cohesion value

Eac = external dynamic earth pressure load

Ei = inertia force


Feq = earthquake loads calculated in accordance with AS 1170.4


G = dead load

GR = part of the dead load tending to resist stability

Gs = specific gravity of the soil

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G1 = dead load of structure

G2 = dead load of fill on structure

G3 = earth pressure due to fill behind structure

G4 = dead load of fill in front of structure

g = gravitational constant (9.81 m/s2)

H = height of wall

= overall height of wall from top to toe of wall at 70 degrees or greater (see ‘Wall

height’ and ‘Wall height for terraces’)

Hw = height of water in front of wall

i = slope angle; or

= stable slope angle


Ip = plasticity index

kA = parameter relating to angularity

kB = parameter relating to grading

kC = parameter relating to density

Ka = static active earth pressure coefficient

Kac = total active earth pressure coefficient (including seismic effects)

kh = horizontal seismic coefficient

kv = vertical seismic coefficient

n = constant representing rate of change of corrosion rate

N ′ = design number of blows from the standard penetration test


Pp = proofload during anchor load

Pw = calculated working load of the anchors (after all losses)

Pwd = resultant dynamic water pressure

Q = live loads (including impact, if any)


Q1 = traffic or other live load on structure

Q2 = traffic or other live load behind structure

Q3 = traffic or other live load in front of structure


R* = design resistance effect

S = site factor for structure in accordance with AS 1170.4

S* = design action effect


Tc = connection strength determined by test

Tcd* = design connection strength

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Tcj* = design connection force at the j

th layer

Td* = design tensile strength of reinforcement

Tdi* = design soil/reinforcement interaction strength

Tij = soil/reinforcement interaction capacity of the reinforcement

Tj* = design maximum tensile force resisted by the j

th layer of reinforcement

Tij* = design soil interaction force at the j

th layer

Tu = short-term ultimate tensile strength

To = original tensile strength

t = time in years


W = weight of the structure and its superstructure

Ws = wind load for strength limit state

Wu = wind load for serviceability limit state

∆Kac = the incremental increase in active earth pressure coefficient

∆T = loss of tensile strength

∆A = loss of section area

θ = arc tan [kh/(1 ± kv)]

δ = external friction angle between soil and structure

φ = characteristic internal friction angle of a soil, which is a parameter in the Mohr-

Coumlomb failure criteria, also referred to as the internal friction angle, or

simply, friction angle

φ′ = effective internal friction angle of a soil

φcv = constant volume internal friction angle of a soil

φr = residual internal friction angle of a soil

φu = undrained internal friction angle of a soil

φ* = design internal friction angle

Φb = partial material reduction factor for anchor bond

Φk = partial importance category factor for anchor pull out

Φt = partial material reduction factor for anchor tendon strength

Φn = structure classification factor

Φr = reduction factor

Φrc = partial material creep reduction factor

Φri = partial material reduction factor due to construction or installation

Φrs = partial material strength reduction factor

Φrt = partial material thickness reduction factor

Φrst = partial material temperature reduction factor

Φu = uncertainty factor for soil/reinforcement interaction

Φua = partial material uncertainty factor for soil/reinforcement interaction

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Φuc = partial design uncertainty factor for cohesion of the soil and backfill materials

Φud = partial material uncertainty factor for overall degradation

Φue = partial material extrapolation uncertainty factor

Φup = partial material product uncertainty factor

Φucon = uncertainty factor for connection strength

Φuφ = partial design uncertainty factor for friction of the soils and backfill materials

ΦR = design capacity of the structural component

γ1 = characteristic value for weight per unit volume of structure

γ2 = characteristic value for weight per unit volume of fill behind structure

γ3 = characteristic value for weight per unit volume of fill above structure

γ4 = characteristic value for weight per unit volume of fill in front of structure

γb = bulk unit weight of the fill behind the wall

γg1 = load factor for γ1




γgw = load factor for γw

γq1 = load factor for Q1



γw = density of water

γm = moist bulk weight in kilonewtons per cubic metre

γs = saturated bulk weight in kilonewtons per cubic metre

ψc = live load combination factor used in assessing the design load for strength limit

state

* = superscript indicates design value (e.g., factored capacity (resistance)) A1

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S E C T I O N 2 I N V E S T I G A T I O N A N D T E S T I N G

2.1 INVESTIGATIONS

2.1.1 Site and geotechnical data

The design of earth-retaining structures requires adequate information on the physical

conditions in the vicinity of the structure including the topography, site layout, nature of

soil, foundation bearing capacity and the ground water conditions (including tidal

conditions when appropriate), together with information on any adjacent structures and

services that may be affected. The investigation shall include an assessment of the regional

geotechnical conditions (e.g. the potential for slope instability) where they may impact on

the proposed development.

All site investigations shall be carried out on the basis of a suitable scope of work, taking

into account the classification of the structure (see Table 1.1 and Table 2.1).

2.1.2 Extent of investigation

The extent and complexity of the site investigations shall be related to the size, complexity

and form of the structure to be designed. Attention shall also be paid to the properties of the

soils in the immediate vicinity of the structure as well as underneath the structure.

The depth of the investigation shall be related to the structure type and size as well as the

site geology. Where appropriate, careful attention shall be paid to both the overall geology

and local geology, including geological defects and discontinuities, bedding planes, joints

and faults. Account shall be taken of conditions such as reactive soils and uncontrolled fill.

Special consideration shall be given to areas of landslip, any tendency of the site to shift,

creep or settle, and areas of possible mine subsidence.

Where a site has been filled, it shall be ascertained whether or not the fill has been placed

as a Class I or Class II ‘controlled fill’ (see Clauses 1.4.3.2 or 1.4.3.3), uncontrolled fill

(see Clause 1.4.3.10) or ‘other fill’ (see Clause 1.4.3.5).

Due to the possibility that even with a careful site investigation unexpected conditions may

be revealed during construction, appropriate inspections shall be carried out during the

course of the construction process to ensure that the conditions revealed during the

construction are in accordance with the assumption made during the design. If the

conditions are not in accordance with these assumptions, then necessary alterations shall be

made to the design to take account of the observed new conditions.

Of special importance to all types of retaining structures is the determination of ground

water, site seepage and surface run off. The investigation of all types of retaining structures

shall include—

(a) a study of the ground water regime in the vicinity of the structure, including sources,

directions of lateral flows, and seasonal or tidal variations;

(b) chemical composition of the ground water; and

(c) the effect of the proposed retaining structure construction on the ground water

regime.

The effect of water discharge from any drains, pipes, and the like on the site conditions

shall also be considered. An assessment should be made of the effects of ground water and

site seepage over the design life of the structure.

2.1.3 General investigation requirements

The extent and amount of detailed information obtained in a particular investigation shall

include the considerations given in Table 2.1. Acc

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TABLE 2.1

INVESTIGATION CONSIDERATIONS

Structure classification Investigation considerations

C B A

Substrata type ● ● ●

Effect of drainage discharge onto surrounding site ● ● ●

Nature of retained material ● ● ●

Site topography ● ● ●

Foundation and embankment strength parameters ● ● ❍

Existing ground water levels and seepage ● ● ❍

Effect of excavations or filling ● ● ❍

Location of existing or proposed adjacent structures ● ● ❍

Effect of modified water table on surrounding site ● ❍ ❍

Global stability ● ❍ ❍

Impact of structure ‘zone of influence’ ● ❍ ❍

Ground movement ● ❍ ❍

● denotes detailed site-specific information required.

❍ denotes only general consideration of the item required.

2.1.4 Investigations for reinforced soil structures

2.1.4.1 General

In addition to the general investigation requirements (see Clause 2.1.3), as the soil material

used in a reinforced soil structure acts as part of the structure itself, consideration shall be

given to the properties of the material that forms the reinforced soil mass.

2.1.4.2 Fill materials

Fill materials for reinforced soil structures shall be selected fill materials, placed and

compacted as a controlled fill (see Clauses 1.4.3.2 and 1.4.3.3).

NOTE: Guidance on the selection of fill material for reinforced soil structures is given in

Appendix D.

2.1.4.3 Fill properties

Where appropriate, testing shall be undertaken to confirm the following properties and

characteristics of the proposed fill:

(a) Physical characteristics (size, grading and the like).

(b) Strength parameters.

(c) Chemical properties.

(d) Electrochemical properties (appropriate when metallic soil reinforcement is

proposed).

(e) Compaction characteristics.

The testing of representative samples shall be carried out in accordance with the relevant

test method of AS 1289 and with any special test procedures defined in this Standard.

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2.1.4.4 Investigations for in situ reinforced soil structures

Additional investigations are required for in situ reinforced soil structures. Where

appropriate, investigations shall include the following:

(a) Identification of the site geology, joints, relic joints, defects, bedding planes, seepage

and water paths, in situ stresses, watertable and the like.

(b) Determination of structural discontinuities and orientation of defects.

(c) Identification of all active and inactive services (e.g. water, sewer, power and

communications) and structures within the ‘zone of influence’ of the structure.

(d) Assessment of the effect of any movement, or deformation, of the reinforced soil

structure on nearby developments or buildings.

2.2 TESTING

2.2.1 Fill materials

Sampling of proposed fill materials for an earth-retaining structure shall be undertaken to

ensure that the samples are truly representative of the materials to be used in the structure

and that their condition duplicates, as far as is practicable, the design conditions in the

actual structure. In particular, materials that are susceptible to crushing under compaction

(e.g. crushed sandstone) shall be pretreated prior to testing to simulate their in-service

condition.

NOTE: Some types of walls need careful attention paid to the type and compaction of the fill in

the wall structure (e.g. crib walls).

2.2.2 In situ materials

Where the properties of in situ materials and existing fill forming the foundations, as well

as the in situ reinforced areas, are critical to the performance or stability of the structure,

then sampling and testing shall be carried out by the relevant undisturbed sampling and

testing procedures set out in AS 1289.

Where the in situ materials or existing fill are suspected to have significant shrink/swell

characteristics (i.e. the site, as defined in AS 2870.1, is a Class M or higher), then the

impact of shrink/swell characteristics of the in situ and fill materials shall be considered.

2.2.3 Laboratory testing

Unless otherwise specified, the laboratory tests shall be undertaken in accordance with the

relevant test method of AS 1289.

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S E C T I O N 3 D E S I G N R E Q U I R E M E N T S

3.1 GENERAL

3.1.1 Introduction

This Section sets out the requirements for the design of earth-retaining structures to ensure

that strength, stability and serviceability are achieved over the intended life of such

structures. Drainage aspects and the influence of construction on the adjacent ground shall

be considered. In the initial design process, the selection of an appropriate retaining

structure shall consider anticipated site conditions, the constructability of the structure and

the need for temporary support measures.

3.1.2 Design principles

For the purpose of reinforced soils and retaining structures design, a limit state is deemed to

be reached when one of the following occurs:

(a) Ultimate limit state (strength and stability)—collapse or major damage as a result of

rupture or instability of the structure, ground, reinforced soils, reinforcement or other

components.

(b) Serviceability limit state—movement or damage in excess of stated design limits.

For both limit states, the design resistance effect (R*) shall be greater than or equal to the

design action effect (S*) for the most critical loads and combinations, i.e.

R* ≥ S

*

where R* and S

* are appropriately factored.

3.1.3 Partial factor method

The requirements of Clauses 3.1, 3.2 and 3.3 are deemed to be met if the requirements of

Sections 4 and 5 are complied with.

3.1.4 Design using other methods

The requirements of Clause 3.1, 3.2 and 3.3 may be met by the adoption of engineering

principles and appropriate loads, resistances and factors.

NOTE: For information on design models and methods see Appendix E.

3.2 DESIGN CONSIDERATIONS FOR ULTIMATE LIMIT STATE

Structure classification (see Table 1.1), design life, durability and maintenance of the

structure shall be considered as part of the design process.

The design for ultimate limit state shall take into consideration, but not necessarily be

limited to, the following six ultimate limit state modes:

(a) Limit Mode U1 Sliding within or at the base of the retaining structure (see

Figure 3.1(A).

(b) Limit Mode U2 Rotation of the structure (see Figure 3.1(B)).

(c) Limit Mode U3 Rupture of components and connections (see Figure 3.1(C)).

(d) Limit Mode U4 Pull-out of reinforcing elements or anchors (see Figure 3.1(D)).

(e) Limit Mode U5 Global failure mechanisms (see Figure 3(E)).

(f) Limit Mode U6 Bearing failure (see Figure 3.1(F)).

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3.3 DESIGN CONSIDERATIONS FOR SERVICEABILITY LIMIT STATE

The design for serviceability limit state shall be adequate in that movement of the

foundation, retaining wall, or reinforced soil structure does not cause local damage to the

structure, which could shorten the structure’s intended life or incur excessive maintenance

costs. Possible deformation modes involving rotation, translation or bulging and settlement

are shown, but not necessarily limited to, the following three serviceability limit state

modes:

(a) Limit Mode S1 Rotation of the structure (see Figure 3.2(A)).

(b) Limit Mode S2 Translation or bulging of the retaining structure (see Figure 3.2(B)).

(c) Limit Mode S3 Settlement of the structure (see Figure 3.2(C)).

The concept of serviceability depends very much on the end use requirements of the

structure. Normally, serviceability requirements for retaining structures are prescribed in

terms of acceptable deformations. These limits will vary with the type of structure. In

addition, the limits required will come into operation at different stages according to the

type of structure.

NOTE: Deformations of reinforced soil structures are influenced as much by the construction

process as by the design.

Post-construction deformations of the structure may be caused by, but not limited to, one or

a combination of the following:

(i) External ground movements (e.g. landslip).

(ii) Foundation settlement.

(iii) Creep extension of synthetic soil reinforcement.

(iv) Creep movement of soil/reinforcement interface.

(v) Consolidation of poorly compacted backfill.

(vi) Displacement and deformation of the facing caused by the likes of construction

equipment loading.

(vii) Deterioration of the reinforcement due to metal corrosion or polymer degradation.

Where soils having significant shrink/swell characteristics are encountered at a site, then

consideration of the effects of the shrink/swell movements shall be taken into account in the

design of the structure.

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NOTE: These diagrams are illustrative of the failure mode.

FIGURE 3.1(A) LIMIT MODE U1: SLIDING—ULTIMATE LIMIT STATE

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FIGURE 3.1(B) LIMIT MODE U2: ROTATION—ULTIMATE LIMIT STATE

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FIGURE 3.1(C) LIMIT MODE U3: RUPTURE OF COMPONENTS AND CONNECTIONS—ULTIMATE LIMIT STATE A

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FIGURE 3.1(D) LIMIT MODE U4: PULL-OUT OF ANCHORS OR REINFORCING ELEMENTS—ULTIMATE LIMIT STATE

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FIGURE 3.1(E) LIMIT MODE U5: GLOBAL FAILURE (WEDGE OR SLIP SURFACE) ULTIMATE LIMIT STATE


FIGURE 3.1(F) LIMIT MODE U5: BEARING FAILURE ULTIMATE LIMIT STATE

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FIGURE 3.2(A) LIMIT MODE S1: ROTATION—SERVICEABILITY LIMIT STATE

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FIGURE 3.2(B) LIMIT MODE S2: TRANSLATION OR BULGING—SERVICEABILITY LIMIT STATE

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FIGURE 3.2(C) LIMIT MODE S3: SETTLEMENT—SERVICEABILITY LIMIT STATE

3.4 DESIGN LIFE

3.4.1 General

Design life shall be considered in the design process.

Each component of an earth-retaining structure shall be durable enough to provide

satisfactory performance over the design life of the structure.

In reinforced soil structures, the life of the reinforcing elements, associated facings and

reinforcement connections shall have compatible durability requirements with the

remainder of the structure, unless the reinforcement is required to function only for a

shorter time while the surrounding ground gains strength.

Typical design life for various applications is given in Table 3.1.

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3.4.2 Design life considerations

For increasing design life, consideration should be given to possible changes over time in

the following:

(a) Loads and load factors.

(b) Material reduction factors appropriate to the structure classification.

(c) Environmental considerations.

(d) Durability and corrosion.

TABLE 3.1

DESIGN LIFE

Design life (years) Typical application

Short

5 Temporary site works

10 Mine structures

Medium

30 Industrial structures

60 River and marine structures, residential

dwellings

90 Minor public works Long

120 Major public works

3.5 DURABILITY AND PERFORMANCE OVER TIME

Durability is the ability of the structure to resist loss of properties or wear such as erosion,

corrosion, creep, chemical, biological and installation damage so that the required strength

is maintained over the design life of the structure. The design shall take into account

changes in relevant properties over time.

NOTES:

1 A check list for investigation of reinforcement products for reinforced soil structures is given

in Table F1, Appendix F.

2 Factors affecting the durability and performance of earth-retaining structure materials are

presented in Table F2, Appendix F.

3.6 DRAINAGE

3.6.1 General

Design of retaining structures shall consider the drainage aspects of the site, including the

short- and long-term subsurface hydrological conditions of the site.

Drainage and the possible development of pore water pressure within a soil are amongst

important considerations in the design of retaining structures because the presence of water

behind an earth-retaining structure has a significant effect on the pressures applied to the

structure. Even when there is no water in direct contact with the structure, increased

pressures can occur on a retaining structure due to an elevated phreatic surface developed

from water seepage into the failure wedge behind the structure.

NOTE: Additional information on drainage measures is given in Appendix G.

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3.6.2 Design considerations

The design of an earth-retaining structure shall carefully consider the effects of water, water

seepage and potential hydrostatic pressures in the design, as well as the long-term

performance of any drainage system installed. In particular, the designer shall consider and

allow for at least the following items in the design:

(a) Existing site ground water conditions and how such conditions are likely to be

affected by the construction of the structure.

(b) Necessity for and specific details of any drainage systems to be provided behind the

structure. Such details would normally include—

(i) the subsurface drainage system, including pipe drains and subsoil drains;

(ii) weep holes;

(iii) filters and geotextiles;

(iv) fill materials;

(v) other drainage details; and

(vi) any associated pipework, clean-out systems and method of drainage efflux.

(c) The ‘long-term’ performance of the drainage system and the necessity for

maintenance.

The design shall be based on the predicted ‘long-term’ condition of the drainage system

rather than the expected performance of the system immediately after installation,

including, if necessary, an assumption of failure or partial failure of the drainage system.

Where clean gravel screenings, pervious materials, geocomposites and the like are specified

by the designer for installation behind the structure, then adequate provisions shall be made

to ensure that surface and stormwater run-off does not overload, foul or clog the subsurface

drainage system.

Where possible, surface water shall be directed away from the top of earth-retaining

structures and not be allowed to pond behind the top of the wall or enter the subsurface

drainage system.

3.7 INFLUENCE OF CONSTRUCTION ON ADJACENT GROUND AND

STRUCTURES

Consideration shall be given to the possible adverse effect on the adjacent land or structures

of the construction of an earth-retaining structure. This is particularly important on sloping

ground where any excavation associated with the construction of the retaining wall may

induce or reactivate slope instability.

3.8 SUBMERGED STRUCTURES

Structures, temporarily or permanently submerged, shall be designed with due consideration

of the effect of static and transient pore water pressures both within and external to the

structure. Other effects such as wave action, water flow and velocity (scour potential),

piping and liquefaction require particular consideration. Typical situations include the

following:

(a) Sea walls.

(b) Reclamation.

(c) Earth bunds.

(d) Abutments for river and creek crossings.

(e) Flood-prone areas.

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For temporarily or permanently submerged or tidally affected structures, consideration shall

be given to the following where appropriate:

(i) Draw-down effects, differential and residual watertables, and tidal lag.

(ii) Piping or material loss from within the structure, the structure backfill or the

foundations.

(iii) Scour or erosion in front of the structure.

(iv) Wave action, including overtopping.

(v) Loss of backfill through the wall due to wave and tidal action.

(vi) Durability of materials.

NOTE: The above factors require particular consideration on a case-by-case basis. The relevant

methodologies are not covered in this Standard and appropriate specialist advice should be

sought.

3.9 CONNECTIONS

The connection of the different elements of an earth-retaining structure shall be designed to

take into account the load-carrying capacity of the connection system. Connections shall be

designed to the same durability criteria as the overall structure and shall be compatible with

the connected elements.

NOTES:

1 The facing of a reinforced soil structure is supported by the reinforced soil mass usually by

connecting directly to the soil reinforcement. The overall stability of the reinforced soil

structure is not necessarily reliant on the stability of the facing system; however, the stability

of the facing system itself relies directly on the connection of the facing elements to the soil

reinforcement elements. The effect of structure movement and load redistribution shall be

considered in the design of the connection.

2 Guidelines for connection design of facings are given in Appendix H.

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S E C T I O N 4 D E S I G N L O A D S

4.1 LOADS

Earth-retaining structures shall be designed for the following loadings and other actions,

during construction and in service:

(a) Dead loads and live loads, including earth pressure and hydrostatic pressure, as

specified in AS 1170.1 except that—

(i) all structures shall be designed for the live loads resulting from the intended use

of the structure but not less than the values given in Table 4.1;

(ii) for the strength and stability limit states, a load factor of 1.0 shall be applied to

water pressure in lieu of the requirement in AS 1170.1 for a load factor of 1.25.

The estimate of the height of the water table shall represent the worst credible

location during the life of the structure; and

(iii) for the strength and stability limit states, the requirement in AS 1170.1 for a

load factor of 1.5 to be applied to earth pressures is deemed to be met by

applying a load factor of 1.25 on the dead loads (including soil weight) and 1.5

on the live loads in combination with the material factors specified in

Clause 5.2 of this Standard.

NOTE: Typically, earth pressure will be calculated by determining the total stresses

deducting the pore water pressure and multiplying the residual by the appropriate load

factor of 1.25.

(iv) Lower partial load factors shall be used where the lower factors lead to a more

critical limit state.

(b) Wind loads as specified in AS 1170.2.

(c) Earthquake loads calculated in accordance with AS 1170.4 and Appendix I.

(d) Other loads that may act on the structure (e.g. snow and ice).

TABLE 4.1

LIVE LOAD kPa

Backfill slope (horizontal/vertical) Classification

Steeper than 4:1 4:1 or flatter

B, C 2.5 5

A 1.5 2.5

4.2 LOAD COMBINATIONS

The load combinations for strength, stability and serviceability shall be as specified in

AS 1170.1. Where a reaction is generated by the application of a factored load, no further

factor shall be applied.

NOTES:

1 For specific applications (such as structures associated with roads and highways), loads, load

factors and loading combinations other than those set out in AS 1170 (all parts) may be

appropriate. If other loads, load factors or loading combinations are used, it may also be

appropriate to vary the associated material factors given in Section 5.

2 Appendix J gives guidance for determination of the appropriate loading combinations in

greater detail than that given in AS 1170.1. The designer should determine whether such

loads, load factors and loading combinations are still valid at the time the design is carried

out.

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3 The load factors specified in AS 1170.1 should be applied to the live loads specified in

Clause 4.1.

4 The dead loads should include—

(a) self weight of the structure;

(b) backfill weight on top of the structure;

(c) imposed earth pressures acting behind the structure;

(d) imposed water pressures acting behind the structure; and

(e) static sill beam loadings (both vertical and horizontal) on earth-retaining structures

designed as bridge abutments.

5 The live loads should include—

(a) traffic surcharge;

(b) bridge vertical live loads acting on the sill beam;

(c) transient loads acting on bridge sill beam, which might include vehicle braking and

thermal effects; and

(d) impact loading.

6 The determination of earthquake design loads should require—

(a) assessment of the seismicity of the site and the potential for liquefaction; and

(b) determination of the response characteristics of the structure.

(c) AS 1170.4 may be used to determine earthquake-induced loadings on structures, taking

into account—

(i) structure classification and related importance factor;

(ii) acceleration coefficient (a); and

(iii) site factor (S).

For the purpose of global stability analysis, the horizontal and vertical distribution of

earthquake-induced forces on the structure may be calculated in accordance with AS 1170.4

and Appendix I, using a static analysis approach, or using a dynamic analysis.

For the purpose of internal stability analysis, the designer should determine the load

distribution and structure resistance behaviour from properly identified dynamic response

characteristics of similar structural systems. Characteristics of structures that need to be taken

into account to differentiate behaviour include facing systems (flexible or stiff) and type of

soil reinforcement (extensible or inextensible).

7 The loads applied by water forces should be taken into account in the design of the structure.

Allowance for the effects of water pressure and buoyancy effects should be made where the

structure is subject to immersion.

8 The design of the structure should allow for the proper drainage of seepage from behind the

structure.

9 This Standard has been drafted with reference to AS 1170.1—1989 for combinations. The

intention is to revise this Standard to be fully consistent with AS/NZS 1170.0.

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S E C T I O N 5 M A T E R I A L D E S I G N F A C T O R S

5.1 GENERAL

This Section sets out the determination and combination of partial material strength design

factors for earth-retaining structures.

Partial design factors for earth-retaining structures are grouped by subscripts as follows:

(a) r—the reduction group of factors (Φr) that cover the effect of identified causes of

decrease in strength and which are drawn from test data.

(b) u—the uncertainty group of factors (Φu) that cover unknowns and uncertainties.

(c) n—the structure classification group of factors (Φn) that cover the consequences of

failure of the particular structure.

For each distinct soil stratum, backfill material or structural component, the design

resistance effect (R*) shall be determined by calculating the material strengths and

resistances based on the characteristic strengths for the material multiplied by Φr, Φu and

Φn.

Soil strengths shall be factored in accordance with Clause 5.2, except where unfactored

values lead to greater critical limit states.

Material strength of structural components shall be factored in accordance with Clause 5.3.

Tensile strength of soil reinforcement shall be factored in accordance with Clause 5.4.

Partial material strength factors shall account for the following:

(i) Variability in the manufactured strengths of the materials.

(ii) Time-dependent stress/strain behaviour.

(iii) Uncertainty of extrapolation of test data.

(iv) Effect of construction-induced damage.

(v) Uncertainties of environmental degradation.

(vi) Time dependent material and strength loss.

An overall structure classification factor shall be applied in accordance with Clause 5.5.

5.2 MATERIAL STRENGTH FACTORS FOR SOIL SHEAR STRENGTH

5.2.1 Cohesion

The partial design factor for the cohesion of the soils and other backfill materials is Φuc (see

Table 5.1(A) and Table 5.1(B)). It shall be applied to c, so that the design cohesion value c*

is given by the following equation:

c* = Φuc c . . . 5.2(1)

5.2.2 Internal friction angle

The partial design factor for the internal friction angle of the soils and other backfill

materials is Φuφ (see Table 5.1(A) and Table 5.1(B)). It shall be applied to ( )φtan , so that

the design internal friction angle φ* is given by the following equation:

φ* = tan

−1 (Φuφ(tanφ)) . . . 5.2(2)

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TABLE 5.1(A)

MATERIAL STRENGTH AND SERVICEABILITY UNCERTAINTY FACTORS FOR

SOIL (based on peak values of c′′′′ and φφφφ′′′′)

Soil or fill conditions

Controlled fill

Soil or material uncertainty

factor

Class I Class II Uncontrolled fill

In situ

material

Φuφ 0.95 0.90 0.75 0.85

Strength Φ

uc 0.90 0.75 0.50 0.70

Φuφ 1.0 0.95 0.90 1.00

Serviceability Φ

uc 1.0 0.85 0.65 0.85

NOTES:

1 Where fill materials defined by the term ‘other fill’ are used, then the partial factors to be used will

depend on the type and quality of the fill materials. In no case shall the partial factor be greater than the

partial factors for Class 1 ‘controlled fill’.

2 The soil strength parameters c′ and φ′ are effective strength parameters. Appendix D gives information

on constant volume and residual strength parameters.

TABLE 5.1(B)

MATERIAL STRENGTH AND SERVICEABILITY UNCERTAINTY FACTORS FOR

SOILS (based on cu and φφφφu)

Soil or fill conditions

Controlled fill Soil or material uncertainty

factor

Class I Class II

Uncontrolled fill In situ

material

Φuφ 0.0 0.0 0.0 0.0

Strength Φ

uc 0.6 0.5 0.3 0.5

Φuφ 0.0 0.0 0.0 0.0

Serviceability Φ

uc 0.9 0.8 0.5 0.75

5.2.3 Determination of c and φ

The characteristic values of c and φ shall be determined by a combination of the following:

(a) Laboratory or field testing or both.

(b) Knowledge of the geological conditions of the site, its stress history and the likely

soil behaviour.

(c) Engineering judgement.

5.3 MATERIAL FACTORS FOR STRUCTURAL COMPONENTS

The structural components of retaining walls, including their connections, shall be designed

in accordance with AS 3600, AS 3700, AS 4100 or AS 1720, as appropriate.

5.4 STRUCTURE CLASSIFICATION FACTOR

The partial design factor to account for structure classification, as defined in Clause 1.2, Φn,

shall be as defined in Table 5.2.

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TABLE 5.2

STRUCTURE CLASSIFICATION DESIGN FACTOR (ΦΦΦΦn)

Design factor, (ΦΦΦΦn)

Structure classification Ultimate limit state Serviceability limit state

C 0.9 1.0

B 1.0 1.0

A 1.1 1.0

NOTE: Depending on the structure classification (see Table 1.1), the consequences of the failure and the

cost of stabilization, it may be necessary to adopt different partial factors to arrive at a practical and

economic solution. Each case has to be assessed on its merits and the assignment of reduced partial

factors, whilst likely to be necessary in some cases, should be carefully judged with respect to the type of

structure and expected performance.

5.5 STRENGTH FACTORS FOR SOIL REINFORCEMENT

5.5.1 Tensile strength of soil reinforcement

5.5.1.1 General

Material strength factors shall be applied to the short-term ultimate tensile capacity of all

soil reinforcement. These factors are related to the properties of the material itself as well

as to construction and environmental effects and are either reduction or uncertainty factors.

Material property factors take into account manufacturing variations and time-dependent

stress/strain behaviour (creep, rupture and extrapolation).

Construction and environmental factors take into account construction damage and

environmental degradation (material loss and strength loss).

The partial material reduction and uncertainty factors are classified in Table 5.3 and

described in this Section.

NOTE: Recommendations for the determination of partial material reduction and uncertainty

factors are set out in Appendix K. The designer should nominate the appropriate factors and their

basis for selection. The determination of reduction factors should be based on adequate test

results. In the absence of test results, the values for reduction factors given in Appendix J should

be used.

TABLE 5.3

MATERIAL REDUCTION AND UNCERTAINTY FACTORS

Factors Manufacturing

Time-dependent

stress/strain

behaviour

Installation

(construction) Environmental

Material reduction

factors — Creep rupture (Φrc) Installation

damage(Φri)

Thickness (Φrt)

Strength (Φrs)

Temperature (Φrst)

Material

uncertainty factors

Product

manufacture (Φup)

Extrapolation (Φue) — Degradation (Φud)

5.5.1.2 Manufacturing variation factor

The short-term ultimate tensile strength (Tu) shall be multiplied by an uncertainty factor

(product) (Φup) which depends on the degree of quality control and whether it is a minimum

or some other characteristic value.

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5.5.1.3 Time-dependent stress/strain behaviour factors

The creep rupture strength is derived from the time at which samples of the reinforcing

product are expected to fail when constantly loaded at a certain percentage of their initial

resistance. The creep rupture strength corresponding to the required minimum service life

shall be the appropriate reference as far as tensile strength is concerned.

For a required service life in excess of the limit of test data, it shall be necessary to carry

out an extrapolation, which is valid only if there is no risk of a transition or ‘knee’ in the

rupture mechanism, knowing that in a log-normal scale diagram the decrease of the creep

rupture strength is represented by a straight line.

The short-term ultimate strength (Tu), shall be multiplied by the following factors:

(a) A partial material creep reduction factor (creep) (Φrc), which is based on test data

conducted at the average estimated in-service temperature.

(b) A partial design uncertainty factor for cohesion of the soil and back fill material

(extrapolation) (Φue), which covers the uncertainties of the extrapolation.

5.5.1.4 Construction damage factor

From manufacture to installation, the strength of the reinforcing product may be reduced

due to—

(a) weathering during the storage period; and

(b) damage due to backfilling and compaction.

The amount of damage depends on the material and structure of the product as well as the

nature of backfill, assuming reasonable compactive effort.

The short-term ultimate tensile strength (Tu) shall be multiplied by a reduction factor

(construction or installation) (Φri), which is based on test data.

5.5.1.5 Environmental degradation factor

All types of reinforcing materials are potentially affected by chemical, biological or

physical actions due to the soil, its constituents, the air and water.

The short-term ultimate tensile strength (Tu) shall be multiplied by the following factors:

(a) A thickness reduction factor (Φrt), which accounts for the diminishing average

thickness or section area of the material and which depends on the required service

life. It typically concerns metallic corrosion, but may also be applied to the

superficial erosion of polymers.

(b) A strength reduction factor (Φrs), which accounts for the loss of strength and which

depends on the required service life. It covers the internal alterations of the material

itself as well as the superficial unevenness, which makes strength decrease more than

the average section area of the material, typically in the case of metals.

(c) A temperature reduction factor (Φrst), which accounts for the loss of strength and

which depends on the temperature of the material during the life of the structure.

(d) An uncertainty factor (overall degradation) (Φud), which depends on the limitation of

knowledge or experience and which covers the unknowns regarding long-term

behaviour.

For strength calculations, a combined reduction factor (Φrt Φrs) may be calculated from a

nominal structural corrosion allowance, normally specified for metals.

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5.5.1.6 Design tensile strength of the soil reinforcement

The design tensile strength of the soil reinforcements shall be determined from the

following equation:

Td* = Tu(Φup)(ΦrcΦue)(Φri)(ΦrtΦrsΦrstΦud)(Φn) . . . 5.5(1)

where

Td* = design tensile strength

Tu = short-term tensile strength

Φup = uncertainty factor (product)

Φrc = reduction factor (creep)

Φue = uncertainty factor (creeptime extrapolation)

Φri = reduction factor (installation)

Φrt = reduction factor (thickness)

Φrs = reduction factor (strength)

Φrst = reduction factor (temperature)

Φud = uncertainty factor ( degradation)

Φn = structure classification factor (see Table 5.2)

The maximum tensile force to be carried by the jth

layer of reinforcement shall not exceed

the design strength of the reinforcement, i.e.

Tj* ≤ Td

*

where

Tj* = design maximum tensile force in the j

th layer

5.5.2 Soil/reinforcement interaction strength

5.5.2.1 General

A material strength factor shall be applied to the soil/reinforcement interaction strength.

This factor shall be assessed by the designer for relevance to the subject soil characteristics

and reinforcement configuration and is an uncertainty factor.

The uncertainty factor for soil/reinforcement interaction shall be Φu.

The appropriate range of values is given in Table 5.4.

TABLE 5.4

MATERIAL STRENGTH FACTORS FOR SOIL/REINFORCEMENT

INTERACTION

Soil reinforcement interaction factors Soil or fill conditions

Strength and

stability load

cases

Serviceability

load case

Φu

(Sliding resistance across reinforcement

surface)

Controlled fill (Class I or II) 0.8 1

Controlled fill (Class I or II) 0.8 1 Φu

(Pull out resistance) Natural or in situ soil 0.75 1

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5.5.2.2 Design soil/reinforcement interaction strength

The design soil/reinforcement interaction strength of the soil reinforcements shall be

determined using the following equation:

Tdi* = TijΦuΦn . . . 5.5(2)

where

Tdi* = design soil/reinforcement interaction strength

Tij = soil/reinforcement interaction capacity of the reinforcement

Φu = uncertainty factor for soil/reinforcement interaction (see Table 5.4)


The maximum interaction force (sliding or pull out) shall not exceed the design soil

interaction strength of the soil reinforcement, that is,

Tij* < Tdi

*

where

Tij* = design soil interaction force at the j

th layer

5.5.3 Connection strength

The design connection strength shall be determined using the following equation:

Tcd* = TcΦuconΦn . . . 5.5(3)

where

Tcd* = design connection strength

Tc = connection strength determined by test

Φucon = uncertainty factor for connection strength = 0.75


The maximum force in the connection shall not exceed the design strength of the

connection, i.e.

Tcj* < Tcd

*

where

Tcd* = connection force at the j

th layer

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S E C T I O N 6 C O N S T R U C T I O N

6.1 GENERAL

All earth-retaining structures covered by this Standard shall be detailed on drawings or

other relevant documents that provide sufficient information to enable them to be

constructed in accordance with designs based on the requirements of Sections 3, 4 and 5.

All construction shall be—

(a) in accordance with the drawings or other relevant documents; and

(b) in compliance with Clauses 6.2 and 6.3.

6.2 CONSTRUCTION TOLERANCES

The designer shall specify construction tolerances that take into account movement during

construction and ensure the intent of the design is not compromised. The requirement is

deemed to be satisfied if the tolerances defined in Table 6.1 and illustrated in Figure 6.1 are

met. If other structures in the vicinity of the wall require closer tolerances, the designer

shall specify appropriate tolerances for the items in Table 6.1 accordingly.

TABLE 6.1

CONSTRUCTION TOLERANCES

Element Vertical

position

Horizontal

position

Vertical

alignment

Horizontal

alignment

Soil surface ±100 mm * * *

Facings and wall structures ±50 mm ±50 mm ±20 mm in 3.0 m ±20 mm in 3.0 m

Footings or supports ±50 mm ±50 mm ±20 mm in 3.0 m ±20 mm in 3.0 m

* Not applicable

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FIGURE 6.1 TOLERANCES

6.3 SPECIFIC REQUIREMENTS

6.3.1 General

In addition to the construction requirements detailed in the drawings and other relevant

documents, the specific requirements given in Clauses 6.3.2 to 6.3.10 shall apply.

6.3.2 Site preparation/excavation

Excavation shall include the removal of all materials necessary for the construction of the

earth-retaining structure.

6.3.3 Foundation soils

The foundation shall be compacted to provide approximately uniform subgrade stiffness

and required bearing capacity. Soft spots shall be removed and replaced with suitable fill.

6.3.4 Footings

When required, a plain concrete levelling pad or footing shall provide a firm, level surface

to facilitate erection of retaining wall units or facing panels.

6.3.5 Fill material

Fill for earth-retaining structures shall comply with the design.

NOTE: Guidelines for fill materials are given in Appendix D.

6.3.6 Placement of fill/compaction

Where fill is to be compacted, the work shall be performed such that the compaction can be

achieved without damaging or dislodging adjacent structures or reinforcement.

6.3.7 Soil reinforcement

Where more than one strength grade of soil reinforcement is to be used, the reinforcement

or ‘bundles’ of reinforcement shall be clearly marked to indicate the strength/grade.

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Soil reinforcement shall be laid and tensioned (if necessary) to avoid excessive deformation

of facing panels. Where layers of soil reinforcement overlap, fill may be required between

these layers.

6.3.8 Facings

Facing panels shall be stored and handled to prevent damage to units. Alignment of units

shall be checked after placement and compaction of fill to ensure units have not been

displaced. Provision shall be made for compressible joint filler where appropriate.

6.3.9 Drainage

Where required by the design, a drainage system shall be provided such that it—

(a) is capable of relieving hydrostatic head behind the structure or within the reinforced

soil mass;

(b) drains freely to a location removed from the structure or reinforced soil mass;

(c) incorporates a means of preventing siltation; and

(d) does not lead to scouring or erosion.

6.3.10 Connections

When required, connections shall ensure a positive and integral connection between facing

elements and soil reinforcement or other anchorages.

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S E C T I O N 7 P E R F O R M A N C E M O N I T O R I N G

The appropriate level of performance monitoring is indicated in Table 7.1. A program for

regular monitoring of retaining structures and stabilized slopes that have been classified in

structure classification C or B shall be recorded and implemented.

TABLE 7.1

MONITORING LEVELS FOR EARTH-RETAINING STRUCTURES

Structure

classification

(see Table 1.1)

Recommended monitoring level

C Regular visual inspection and inspections after events such as floods or earthquakes.

Monitoring of vertical and horizontal deformations, flows from drainage system,

possibly pore pressures, earth pressures and stresses in selected soil-reinforcing

elements and anchors. Check on corrosion or degradation of soil reinforcing materials

(e.g. exhuming of dummy reinforcing elements embedded in the backfill during

construction)

B Regular visual inspection and inspections after events such as floods or earthquakes.

Includes check of effectiveness of the drainage system. Basic monitoring of lateral

deformation

A No monitoring required

NOTES:

1 Basic indicators of the performance of earth structures are—

(a) lateral deformation; and

(b) settlement.

2 A visual inspection should detect excessive movement, cracks or ruptures, lack of drainage capacity,

physical changes and changes in the environmental conditions.

3 Where a wall is evidencing structural distress, to assess the degree of instability and to assist in the

selection of remedial measures, the following could also be considered:

(a) Seepage flows (including flows from drainage pipes).

(b) Pore pressures.

(c) Vertical earth pressures.

(d) Lateral earth pressures.

(e) Vibrations.

(f) Stresses in structural components (including reinforcing elements).

(g) Rate of corrosion or chemical degradation of reinforcing strips and meshes.

(h) Temperature.

(i) Any other factor considered likely to affect performance.

4 Inspections carried out once per year could be considered to be ‘regular’ for purposes of this table.

5 The purpose of monitoring is to ensure one or both of the following objectives:

(a) Ensuring the safety of the structure.

(b) Checking assumptions and predictions of the design.

6 Contributing to data, which in the longer term will lead to an improvement in design procedures.

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APPENDIX A

STRUCTURE CLASSIFICATION

(Informative)

A1 GENERAL

Clause 1.2 requires earth-retaining structures to be classified according to Table 1.1. For

such structures, the classification should be assessed with respect to likely consequences of

structure failure.

A2 STRUCTURE FAILURE CONSEQUENCE

The consequence of structure failure is related to the loading type and its location on the

structure, as well as the relationship between the wall slope and geometry and associated

structures and facilities.

(a) The structure should or damage to associated structures or facilities?

(b) What is the likely loss of use of function or facility?

(c) What is the possibility of injury to people?

(d) What is the likely size and weight of facing elements?

(e) What is the height of wall?

(f) What is the proximity of nearby structures?

For a reinforced earth- be classified according to the consequences of structure failure by

considering the following questions (see Table 1.1):

What is the likely loss retaining structure, the classification should be assessed with respect

to the consequences of failure with reference to the location of facilities on top, or at the

base, and the structure geometry as shown in Figure A1.

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3

2

tm

φαθ +=

5

32

tfb

φαθθ +==

NOTE: Structures beyond the base limit or beyond the top limit are unlikely to be affected by, or have an effect on, the

structure classification.

FIGURE A1 WALL SLOPE AND GEOMETRY

A3 GUIDANCE ON CLASSIFICATION OF STRUCTURES

Table A1 gives examples of the classification of earth-retaining structures.

Table A2 gives a general method for classifying an earth-retaining structure according to

the human life and other consequences arising from the failure of the structure. For

example, a low wall supporting a road that is the only access to a major hospital might have

high social consequences in the event of a failure, even though it is inexpensive to repair,

and its failure would not in itself constitute a high risk to life. The consequences of failure

during events such as earthquakes or cyclones might be relevant in this case.

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TABLE A1

EXAMPLES OF STRUCTURE CLASSIFICATION

Classification Description Examples

Where failure would result in minimal damage

and loss of access:

A Low consequence for loss of human life, or

small or moderate economic, social or

environmental consequences Walls in areas rarely visited by people

Walls on private property supporting

gardens, fences, etc.

Where failure would result in moderate damage

and loss of services:

B Medium consequence for loss of human

life, or

considerable economic, social or

environmental consequences Walls not included in classifications A or C

Walls supporting or above normal structures

Walls supporting minor roads

Walls above public spaces

Walls with height ≥1.5 m

Where failure would result in significant

damage or risk to life:

C High consequence for loss of human life,

or

very great economic, social or

environmental consequences Walls supporting structures identified for

post-disaster recovery

Walls supporting or above access or

services to structures identified for post-

disaster recovery

TABLE A2

GENERAL METHOD FOR STRUCTURE CLASSIFICATION

Risk to life Public impact

(economic, social or environmental) Low Medium High

Low A B B

Medium B B C

High B C C

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APPENDIX B

GROUND ANCHORS

(Informative)

B1 GENERAL

The term ground anchor refers to a tensile reinforcement, which may typically be a high

tensile steel strand, wire, bar or high-strength polymer, placed in a hole drilled at an aspect

into a foundation material. Whilst this Appendix sets out guidelines for the classification

and design of ground anchors, the notes provided in this Appendix should not prevent the

use of alternative designs and materials in accordance with engineering principles.

The relevant sections of these guidelines are also applicable to the design and installation of

rock bolts, soil nails and dowels.

B2 ANCHOR COMPONENTS

Anchors generally have the parts as illustrated in Figures B1 and B2. The parts are defined

as follows:

(a) Anchor head—a device, usually consisting of a bearing plate and head or nut assembly

which permits the stressing and lock-off of the anchor tendon or bar.

(b) Tendon—a tensile reinforcement used to transfer load from the anchor head to the

anchorage zone, which may consist of high-tensile steel tendon, wire strand or bar.

The anchor may also be of polymer materials.

(c) Anchorage—that section of the tendon which is bonded, or otherwise secured, in the

anchorage zone.

(d) Bond length (grouted anchors only)—that portion of the anchor fixed in the grout

bulb through which load is transferred to the surrounding soil or rock.

(e) Bond zone (mechanically anchored anchors only)—that portion of the anchorage zone

in which the load is transferred from the plate or expansion anchor into the

surrounding soil or rock.

(f) Free length—the unbonded length of the anchor, which is free to elongate elastically

and transmit the resisting force from the anchorage zone to the structural element via

the anchor head.

(g) Grout—either a cement-based mixture, which may include additives, or a specially

formulated chemical compound (e.g. epoxy resin).

NOTES:

1 In grouted anchors, the grout also transfers load from the tendon to the soil or rock.

2 In some temporary anchor installations, the anchor-free length may not be grouted.

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FIGURE B1 GROUND ANCHOR TERMINOLOGY (GROUTED ANCHORAGE)

FIGURE B2 GROUND ANCHOR TERMINOLOGY (MECHANICAL ANCHORAGE)

B3 TYPE OF ANCHORS

B3.1 Permanent anchors

An anchor installation that is required to ensure the stability and satisfactory performance

of the permanent structure being supported.

B3.2 Temporary anchors

An anchor installation designed for a short project life, usually 5 years (see Table 3.1).

B4 DESIGN

B4.1 General

The design of the anchors should take into account—

(a) the movement possibilities of the structure;

(b) the rigidity of the structure;

(c) the compatibility of the movements of the anchors and the anchored zone;

(d) the behaviour of the ground under stressing loads;

(e) anisotropy, inhomogeneity and discountinuties of the rock;

(f) overall stability and failure mechanisms; and

(g) their design life (see Table 3.1).

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NOTES:

1 These design considerations are also applicable to rock bolts, soil nails and dowels.

2 The state of the art for ground anchors has not yet progressed to the point where the

application of formulae can necessarily ensure adequate capacity. As such, whilst anchor

capacities can be estimated from bond lengths and load transfer to the anchorage zone, the

service and design loads should be verified by testing each production anchor to assure

load capacity.

3 Where appropriate regular checks of anchor loads should be made.

B4.2 Design of anchors with a rock anchorage zone

B4.2.1 General

The determination of the details of the anchorage, bond and anchor free length requires

consideration of—

(a) uplift resistance of rock mass;

(b) tendon design;

(c) rock to grout bond and grout to tendon bond (grouted anchors);

(d) soil to tendon bond for soil nails or soil reinforcement; and

(e) strength of mechanical anchorage for mechanically secured anchors.

B4.2.2 Uplift resistance of rock mass

For an isolated vertical anchor, the uplift resistance may be equated to the weight of an

inverted cone of rock having either a base angle of 60° or 90° when measured from the

middle of the bond length or of a cone having a base angle of 60° or 90° and measured from

the bottom of the anchor grout as shown in Figure B3. The 60° angle is to be used when the

rock mass is soft, heavily fissured or weathered. Where the anchor is below the water table,

the buoyant weight of the rock shall be used. In either case, the mass of the cone has to be

sufficient to balance a test force of 85% of the characteristic ultimate tensile resistance of

the tendon. With the inclusion of the rock shear resistance, the anchorage should be able to

develop the characteristic ultimate tensile resistance of the tendon, but care has to be

exercised in highly fissured rock, especially when high pore water pressures occur.

For multiple anchors at close centres, the rock cones may intersect and a wedge-shaped

rock section should be considered for resistance calculations.

For a concentrated anchor layout where the fixed ground anchors are spaced at less than

0.5 times the fixed anchor length, it is recommended that a vertical stagger of 0.5 times the

fixed anchor length be used to prevent possible laminar separation of the rock.

The resistance of the rock to anchorage loads should in all cases be evaluated in

conjunction with adequate field and laboratory investigation and testing. Lesser anchorage

depths may be used where it can be demonstrated that the required forces can be achieved.

In the case of horizontal anchors, the anchorage should be located so that the tendon crosses

any known plane of failure and the pull-out capacity should be calculated from the

principles of rock mechanics.

A minimum fixed anchor length of 3 m is recommended to guard against variable rock

quality and constructional imperfections.

The design resistance effect should be greater than the design action effect. For the case

involving dead and live loadings, the requirements may be expressed by the following:

S* ≤ 0.8ΦnΦkG

R

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where

GR = part of the dead loading tending to resist instability

Φk = see Table B1

Φn = see Table 5.2

Further details on the application of load combinations are given in Appendix I.

TABLE B1

MINIMUM PROOF LOAD

Anchor category

Importance

category

reduction factor

ΦΦΦΦk

Minimum proof

load/working

load W

P

P

P

1 Temporary anchors where the service life is less than six

months of a structure classification A structure, that is,

where failure would have few serious consequences and

would not endanger public safety, e.g. short-term pile test

loading using anchors as a reaction system

0.9 1.1

2 Temporary anchors with a service life of up to five years

of a structure classification B structure, that is, where,

although the consequences of load failure are quite

serious, there is no danger to public safety without

adequate warning, e.g. retaining wall tie backs

0.85 1.25

3 Any permanent anchors and also temporary anchors of a

structure classification C structure, that is, where the

consequences of failure are serious, e.g. temporary

anchors for main cables of a suspension bridge, or as a

reaction for lifting heavy structural members

0.8 1.5

NOTE: For class of structure refer to Table 1.1.

TABLE B2

MINIMUM MATERIAL REDUCTION FACTORS

Φt Tendons 0.9

Φb Bond 0.7

B4.2.3 Rock to grout bond

Bond at the rock to grout interface may be considered as uniformly distributed along the

bond length for design purposes. In reality, however, the load is carried non-uniformly with

a maximum transfer stress at the junction of the free and bond lengths, diminishing quickly

towards the distant end of the bond length.

When shear strength tests are carried out on representative samples of the rock mass, due

allowance should be made for in-place joints or other defects, the average effective design

bond stress not exceeding the minimum shear strength of the rock multiplied by the relevant

material factors and importance factors specified in Tables B1 and B2.

In the absence of shear strength data or pull-out tests refer to Table B3 for typical values of

characteristic ultimate rock-to-grout bond stresses.

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A minimum fixed anchor length of 3 m is recommended to guard against variable rock

quality and constructional imperfections.

Experience has shown that increasing bond length beyond 10 to 12 m does not result in

increased load capacity.

Weathering degree, degree of mineral bond and distance of disjunction surfaces are three

conditions with the most unfavourable condition being decisive.

FIGURE B3 TRANSIENT LOADING IN ROCK

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TABLE B3

ULTIMATE BOND STRESSES FOR ROCK ANCHORS (MPa) (OSTERMAYER)

Rock type

Condition Igneous and

metamorphic

Conglomerate and

breccia Argillaceous sediments

Weathering degree

(see AS 1726)

Mineral bond

Distance of disjunction

surfaces

Granite, gabbro,

basalt, tuff, diorite,

gneiss, schist, slate,

quartzite

Sandstone,

limestone, chalk,

dolomite, stone

Marl, shale, claystone,

mudstone, siltstone

Unweathered (FR)

Very good mineral bond

More than 0.3 m

4.0 2.7 1.7

Weathered (SW)

Good mineral bond

Between 0.1 and 0.3 m

2.5 1.9 1.0

Distinctly weathered (DW)

Poor mineral bond

Less than 0.1 m

1.3 0.8 0.4

NOTE: For weathered rock description, see AS 1726.

B4.2.4 Grout to tendon bond

The characteristic ultimate value of bond resistance may be taken as—

(a) 1.0 MPa for clean wire tendons; and

(b) 2.0 MPa for clean strand tendons.

For strand tendons, the effective area for bond should be taken as the surface area of a

smoother cylinder having a diameter equal to the nominal diameter of the strand.

For bar tendons, the bond may be improved by using the nuts and washers in the bond

length, with anchorage lengths determined by actual test.

For strand tendons, a weave pattern in the bond should increase bond resistance.

The relevant materials factor specified in Table B2 should be applied to the above values.

B4.2.5 Tendon design

Tendons for rock anchors should be designed such that—

S* < ΦkΦnΦtfpAp . . . .B4(1)

where

fp = tensile strength of the tendon

Ap = cross-sectional area of tendon

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B4.3 Design of soil anchors (including soil nails)

Anchorage resistance should be determined generally as for rock anchors except that soil

grout bond length may be estimated as follows:

(a) For bulb type anchors (see Figure B4) formed by high pressure grouting, the design

ultimate pull-out resistance may be determined from the following equation.

Tl* = ΦnΦbNlLftanφ*

. . . B4(2)

Values of N1 are 130 to 160 kN/m of fixed anchor length.

(b) For multi-under-reamed anchorage (see Paragraph B3) in stiff cohesive soils with

bells at 3D centres, design ultimate pull-out resistance may be determined as—

Tl* = ΦbDLfc

* . . . B4(3)

where

Lf = fixed anchor length

D = diameter of bell of under-reamed ground anchor

Both these equations are simple but crude. A more accurate estimate can be obtained by

taking into account factors such as contact pressure at the fixed anchor/soil interface,

effective overburden pressure and end-bearing capacity.

Where inclined or horizontal plate anchors are used, the evaluation of the capacity of the

anchor is more complex and will depend on the shape of the anchor, as well as its depth and

the material properties.

FIGURE B4 TYPES OF SOIL ANCHOR

B4.4 Anchorage loads

For a ground anchor to function effectively, it is important that the designer specify the

following:

(a) PW—the required anchor working load.

(b) PP—the anchor proof (or test) load.

(c) PLO—the anchor ‘lock-off’ load.

(d) PLT—the long-term design load in the ground anchor.

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These are more fully described as follows:

(i) PW—the working load necessary to ensure that the structure behaves in a satisfactory

manner. Under normal circumstances working loads should not exceed 60% of the

characteristic yield strength of the tendon. In some situations (e.g. temporary anchors)

it may be acceptable to load the tendon to 65% of the characteristic strength of the

tendon. The above values apply to anchors manufactured of steel. For anchors

manufactured of polymers, the designer should select appropriate values.

(ii) PP—proof load to which the ground anchor is to be loaded to check the adequacy

(see Table B1 for minimum proof load to working load factors).

(iii) PLO—the lock-off load, which will be left in the ground anchor when stressed.

NOTES:

1 The lock-off load should not exceed 75% of the characteristic yield strength of the

tendon.

2 In some applications the lock-off load will be very much less than PW.

(iv) PLT—the long-term load in the anchorage, which will exist in the anchorage as a

result of its construction, prestressing, creep and subsequent ground movements.

NOTE: PLT should be greater than or equal to PW.

B4.5 Testing of anchors

All anchors should be ‘proof load’ tested during installation. The minimum proof load test

should consist of—

(a) stressing of the anchor to the required ‘proof load’ and holding at that load for at least

15 min; and

(b) relaxing of the anchor to the specified ‘lock off’ load.

If an anchor fails to hold the proof load for the required time, then the anchor should be

deemed to have failed, or the test result referred to the designer for comment and

verification of capacity.

B4.6 Anchor technical description

The designer of a ground anchor should nominate the following as a minimum:

(a) Type of anchor (i.e. temporary or permanent) and the design life.

(b) Expected anchorage zone material for the anchor.

(c) Minimum free length.

(d) Ultimate design load.

(e) Test proof load and loading duration.

(f) Lock-off load.

B5 CORROSION PROTECTION

The tendon anchorage and anchor head arrangement has to be given adequate corrosion

protection, which has to remain effective throughout the design service life of the

anchorage. The effectiveness of the protection should not be impaired during storage,

transport, installation and stressing of the anchorage. Proof of the suitability of the

corrosion protection system should be supplied.

For permanent grouted anchors, the corrosion protection system should be fully

encapsulated in polyethylene sheathing or better. The only exception, in special

circumstances, is the use of prestressing bars coated with epoxy coating. Whilst corrosion

protection by cement grout is usually sufficient for temporary anchors, in aggressive ground

conditions it may be necessary to fully encapsulate the anchor. A film of rust on the tendon

is not necessarily harmful and may improve the grout to tendon bond but any form of

pitting is unacceptable.

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APPENDIX C

SOIL NAILING FOR EARTH-RETAINING STRUCTURES

(Informative)

C1 GENERAL

Soil nailing may be used for the construction of either temporary or permanent walls or for

stabilizing walls formed in cut.

Constructing a soil-nailed wall involves reinforcing an exposed excavated face as work

proceeds. The reinforcing consists of introducing a pattern of passive bars that essentially

work in tension; these are usually installed normal to the face or inclined slightly

downward.

Using this method and working from the top down, a mass of reinforced soil is gradually

created. In order to avoid the soil between the points of reinforcement becoming unstable,

some form of facing needs to be installed; this is generally achieved with reinforced

shotcrete. The facing can be vertical or battered and can include benches (see Figure C1).

Once constructed, a soil-nailed wall shows a certain similarity with a reinforced-soil wall.

The fact that a soil-nailed wall will have been built downward by progressive excavation

and nailing, with the soil being reinforced in situ, and a reinforced soil wall is constructed

by placing successive layers of fill and reinforcement, constitutes an essential difference.

Nails can be installed in two principle ways—

(a) either by drilling and then grouting with cement grout or mortar in a pre-drilled hole;

or

(b) by either percussive methods, vibro-drilling or ballistic techniques.

Soil nailing techniques are also well-suited to retaining-wall strengthening and repair.

Nails are generally made of steel, although other materials have been used.

The facing wall is generally constructed of sprayed concrete, although some installations

have used soft (e.g. chain wire mesh) facings.

In the case of a facing wall of reinforced sprayed concrete, the thickness depends mainly on

the grid layout of the nails, pull out forces at the nail head and corrosion considerations.

Unlike other reinforced soil techniques, the building of a soil nailed wall has several critical

phases, viz.

(i) local excavation stability during each earthworks excavation stage prior to the

installation of nails;

(ii) overall excavation/partially completed wall stability during the excavation for a

particular stage; and

(iii) the completed wall.

Each of these stages requires careful analysis by a designer. Also, the installation of

drainage within and behind the facing of a soil nail wall requires careful detailing.

State-of-the-art techniques and design methods are reviewed elsewhere, (see Refs 1, 2

and 3). Details of field performance are given in the French national research project

‘Clouterre’, (Ref. 4).

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C2 BASIS FOR DESIGN

Soil nailing has much in common with conventional reinforced soil in that the reinforcing

members are generally used to provide tensile resistance. The principal applications of soil

nailing have been the construction of new slopes in cuttings, or as remedial works to

unstable or potentially unstable slopes, (Refs 2, 4, 5, 6, 8 and 9) and structures (Ref. 12).

As soil nailing is a process of installing dowel type soil anchors that are not tensioned, it is

important that the following be observed:

(a) The dowel type anchors ‘self-tension’ under load. Consequently, the nails should be

installed at an angle to the predicted active wedge shear plane which allows this ‘self-

tensioning’ to occur. This normally requires the nails to be installed at angles of less

than 15° to the horizontal.

(b) The nails are provided with a secure connection to the facing material; the strength of

this connection should be as set out in Table G2 of Appendix G.

(c) The nails are in line with the suggestions on ground anchors (rock bolts and dowels)

set out in Appendix B.

In its final configuration, a soil-nailed structure is similar to a conventional fill-reinforced

soil structure. However, there are important differences in construction, particularly as the

nails are inserted directly into an existing mass of earth rather than installed with the fill, as

is the case for a reinforced soil structure (see Figure C2).

Furthermore, the construction process for excavated faces is such that the upper nails are

loaded first, in contrast to a reinforced soil wall in which the lower reinforcements are

loaded first. These different construction procedures thus influence the transient

distribution of loads, and thus the required strength of the various reinforcing elements.

C3 LIMIT STATES

The ultimate limit states for soil-nailed walls are similar to those listed for reinforced fill

walls. However, as a critical condition for a soil-nailed structure can occur during the

staged excavation/nailed installation process this condition is an important ‘Limit State’.

The serviceability limit states for soil-nailed walls are similar to those for reinforced soil

slopes and walls. In soil nailing, however, there will be some movement of the nailed mass

of earth in order to generate the tensile and shear stresses required for stability.

C4 EXTERNAL STABILITY

External stability considerations for nailed walls are similar to those for reinforced fill

slopes and walls.

C5 INTERNAL STABILITY

C5.1 General

All soil reinforcement systems, including soil nailing, have considerable scope for

redistribution of load between elements. Thus, if an element is overloaded, by attaining

limiting friction, it can slip and redistribute the excess load to others. A further safeguard

with a soil-nailing system is that additional nails can be provided if movement of this

structure is greater than anticipated.

Internal failure of a soil-nailed structure is assumed to result from quasi-rigid body rotation

and two zones can be distinguished, an active zone, and a resistant zone, which are

separated by a slip surface along which movement takes place. The surface has to be

kinematically admissible, and the relative geometrical movements have to be feasible.

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Several forms of failure surface have been proposed including wedge, two-part wedge,

circular slip and log-spiral. Loads are induced in the nails, which extend into the resisting

zone providing support for the active zone. The tensile and shearing forces in the nails

should provide the restoring component to the out-of-balance force or moment between the

disturbing forces and the available internal friction angle of the soil.

Although the model of deformation is usually taken to be two-dimensional, in some cases it

may be three dimensional; for example, with skew nailing or where the nailed structure

changes direction in plan.

The stages of a design usually involve the following:

(a) The determination of the position of the critical slip surface, and the resisting force or

moment required to maintain the equilibrium of the active zone.

(b) The determination of the tensile and shear loads for an initial constant spacing and

inclination of nails of constant stiffness and length.

(c) A check for each level, allowing for the stages of construction, against failure due to

each of the following listed limit states:

(i) Tension in the nail at the slip surface.

(ii) Pull-out of the length of nail in the resistant zone.

(iii) Bending and shear in the nail near the slip surface.

(iv) Bearing failure of soil against the nail.

(d) The selection of a new and improved pattern and disposition of nails and re-analysis.

It is necessary, particularly for the construction of new slopes, to ensure that unsupported

heights can withstand temporary forces.

C5.2 Methods of assessing internal stability

A procedure should be selected, which should ensure that the most critical failure surfaces

are determined. Methods that are commonly used correspond to those generally applied for

stability analyses of slopes, although other failure surfaces may be employed.

Where soil nailing is being used as a remedial measure in an unstable slope, attention

should be paid to any existing failure surfaces. The geometry of the failure surface should

be determined and relevant shear strength parameters used, including residual values where

appropriate, to assess stability in these circumstances.

In the assessment of internal stability, the shear resistance of the nails may be significant

(about 5%), in contrast to the usual reinforced soil structure. This is because in a reinforced

soil structure built of fill materials, it is usual to use flexible reinforcements, which can

only carry tension, and thus shear is neglected.

A number of techniques for analysing the stability of nailed slopes have been proposed, the

most commonly used being the two-part wedge and log-spiral methods.

C5.3 Checks for nail loading

Where the nails are designed to act in tension only, a check against rupture, bond failure in

the resistant zone, and bond failure in the active zone should be undertaken. Where the nails

are subjected to the combined effect of tension and shear, reference may be made to RDGC

(Ref. 4), Bridle and Bar (Ref. 13) or Jewell (Ref. 9).

C6 SERVICEABILITY

The serviceability limits governing the internal stability of a soil-nailed structure are similar

to those for a reinforced soil structure. Where special concrete facings are used, any excess

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NOTE: An advantage of soil nailing is that extra nails may be inserted into the structure to

control observed deformations (at any time following construction) that are in excess of those

specified.

C7 FACINGS

The most common form of facing for a soil-nailed structure is sprayed concrete applied

progressively as the soil nail wall is constructed. In permanent structures, the sprayed

concrete is often applied in a two-stage process, to ensure adequate concrete cover and

corrosion protection to reinforcement. The two-stage process also greatly simplifies anchor

head design and tensioning. The purpose of the sprayed concrete facing is primarily to

distribute the soil wall anchor head loads over the exposed face and support the soil near

the face between the anchor.

A variety of precast concrete facings have also been used as wall facing.

Flexible or soft facings (e.g. geogrids, catenary cables, etc.) have also been used for soil-

nailed structures where they have the advantage of allowing the slope to be vegetated.

These systems are however normally only effective in ‘weathered rock’ soil-nailed

structures.

C8 REFERENCES

1 GASSLER, G., In-Situ Techniques of Reinforced Soil, Performance of Reinforced Soil

Structures, edited by McGown, A., Yeo, K.C., and Andrews, K.Z., Glasgow, Thomas

Telford, 1990, pp. 185-196.

2 SCHLOSSER, F., Behaviour and Design of Soil Nailing, Proceedings International

Symposium on Recent Developments in Ground Improvement Techniques, Bangkok,

Balkema, 1982, pp. 399-413.

3 SCHLOSSER, F., and DE BUHAN, P., Theory and Design Related to the

Performance of Reinforced Soil Structures, State-of-the-Art Review, Performance of

Reinforced Soil Structures, edited by McGown, A., Yeo, K.C., and Andrews, K.Z.,

Glasgow, Thomas Telford, 1990, pp. 1-14.

4 RDGC, Reinforcement des Sols par Clouage: Programme Clouterre, Projets

Nationaux de Recherche Development en Genie Civil, Paris, February 1991.

5 GUILLOUX, A., and SCHLOSSER, F., Soil Nailing: Practical Applications,

Proceedings International Symposium on Recent Developments in Ground

Improvement Techniques, Bangkok, Balkerma, 1982, pp 389-398.

6 CARTIER, G., Examples of the Use of Soil Nailing for the Stabilization of Unstable

Slopes, Bulletin Liaisons Laboratoire Central des Ponts et Chaussees, 1986, 145,

pp. 5-12.

7 BRUCE, D.A., and JEWELL, R.A., Soil Nailing; Application and Practice—Part 1,

Ground Engineering, 1986, Vol. 19, 9910-15.

8 BRUCE, D.A., and JEWELL, R.A., Soil Nailing, Application and Practice—Part 2,

Ground Engineering, 1987, Vol. 20, pp. 21-38.

9 JEWELL, R.A., Soil Nailing, General Report Performance of Reinforced Soil

Structures, edited by McGown, A., Yeo, K.C., and Andrews, K.Z., Glasgow, Thomas

Telford, 1990, pp. 197-200.

10 BRIDLE, R.J., and MYLES, B., A Machine for Soil Nailing—Process and design,

Ecole Nationale des Ponts et Chaussees, Paris, October 1991.

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11 STOCKER, M.F., KORBER, G.W., GASSLER, G., and GUDEHUS, G., Soil Nailing,

Proceedings International Conference on Soil Reinforcement: Reinforced Earth and

Other Techniques, Ecole Nationale des Ponts et Chaussees, Paris, October 1979,

pp. 469-474.

12 BANG, S., SHEN, C.K. and ROMSTAD, K.M., Analysis of Earth reinforcing System

for Deep Excavation. Transportation Research Record 749, National Academy of

Sciences, Washington, 1980.

13 BRIDLE, R.J., and BARR, B.I.G., The Analysis and Design of Soil Nails,

Performance of Reinforced Soil Structures, edited by McGown, A., Yeo, K.C., and

Andrewes, K.Z., Glasgow, Thomas Telford, 1990, pp. 249-254.

FIGURE C1 SOIL-NAILED WALLS

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FIGURE C2 APPLICATIONS OF SOIL-NAILING

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APPENDIX D

SOIL AND MATERIAL PROPERTIES

(Informative)

D1 GENERAL

The design of earth-retaining structures is usually based on effective strength parameters.

The material reduction factors recommended in this Standard are applied to both the

effective strength parameters c′ and φ′ and, if used, the undrained shear strength cu (φu = 0).

If constant volume or residual values (φcu and φr respectively) are used, a different reduction

factor would be appropriate.

The selection of a representative value of a soil parameter should take into account the

various matters referred to in Section 2 and determined as part of the site investigation

process.

The assessment of the relevant soil parameter is often dependent upon the mechanism, or

mode of deformation (or limit state) being considered for the retaining structure. For

example, different representative strengths will be required for a shear failure in a fissured

material, depending upon whether the shear surface is free to follow the fissures, or is

constrained to intersect intact material. A range of values should also be considered if the

soil parameters are likely to change during the lifetime of the retaining structure.

The soil properties may also be assessed or amplified by data from ‘back analysis’ of

comparable retaining structures or experience with similar ground conditions.

For anchored walls and in situ reinforced soil structures, the shear resistance between the

anchor/soil nail/dowel and the in situ material is a critical design parameter. Assessment of

the interface shear strength depends on and has to take into account the following:

(a) Installation method.

(b) Type of grout, mix design and injection technique.

(c) In situ material properties.

NOTE: In some published literature the soil/reinforcement interface shear strength is also termed

‘bond strength’.

For reinforced soil structures, tests may be required to determine the following:

(i) Soil/reinforcement interface shear strength.

(ii) Soil/reinforcement pull-out strength.

(iii) Shear strength of fill.

Particular care should be taken in the selection of a test method to correlate the sample size

to the parameter being tested, and that the testing apparatus is of sufficient size to properly

represent the field service condition.

D2 SOIL PARAMETERS

D2.1 Soil unit weights

Typical unit weights for a variety of soil materials are set out in Table D1 and may be used

in the absence of reliable test results.

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D2.2 Soil friction (φφφφ) and cohesion (c)

D2.2.1 General

Figure D1, Tables D2, D3 and D4 provide guidance on various empirical relationships

between classification and index tests for representative values of φ and c for both cohesive

and cohesionless materials.

D2.2.2 Cohesive soils

The undrained shear strength of a clay soil is not a reliable soil parameter. Different values

may be recorded in triaxial compression and extension, direct shear and in pressure meter

tests in situ. Further, the undrained strength of a soft clay with a small over-consolidation

ratio (say, less than 3) increases when the positive pore water pressure dissipates.

In assessing the strength of soil, it is important to consider the likely moisture environment

of the earth-retaining structure, as well as questions such as those dealing with clay

sensitivity, strength reduction on remoulding, failure envelope and whether large strains can

occur, which could result in the development of either the residual or critical state angle of

shear resistance.

TABLE D1

UNIT WEIGHTS OF SOILS (AND SIMILAR MATERIALS)

γγγγm: moist bulk weight (kN/m3) γγγγs: saturated bulk weight (kN/m3) Material

Loose Dense Loose Dense

A—Granular

Gravel 16.0 18.0 20.0 21.0

Well-graded sand and gravel 19.0 21.0 21.5 23.0

Coarse or medium sand 16.5 18.5 20.0 21.5

Well-graded sand 18.0 21.0 20.5 22.5

Fine or silty sand 17.0 19.0 20.0 21.5

Rock fill 15.0 17.5 19.5 21.0

Brick hardcore 13.0 17.5 16.5 19.0

Slag fill 12.0 15.0 18.0 20.0

Ash fill 6.5 10.0 13.0 15.0

B—Cohesive

Peat (very variable) 12.0 12.0

Organic clay 15.0 15.0

Soft clay 17.0 17.0

Firm clay 18.0 18.0

Stiff clay 19.0 19.0

Hard clay 20.0 20.0

Stiff or hard glacial clay 21.0 21.0

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NOTE: Approximately 80% of data falls within one standard deviation. Only a few extreme scatter values are shown

(Data from several sources: Ladd et al. (1977), Bjerrum and Simons (1960), Kanja and Wolle (1977), Olsen et al.

(1986).)

FIGURE D1 CORRELATION BETWEEN φ′ AND PLASTICITY INDEX Ip FOR NORMALLY

CONSOLIDATED (INCLUDING MARINE) CLAYS

D2.2.3 Cohesionless soils

The strength and stiffness of cohesionless soils vary with respect to density, angularity and

grading of particles. An estimation for characteristic peak effective internal friction angle

φ′ can be given by—

φ′ = 30 + kA + kB + kC . . . D1

where the parameters kA, kB and kC relate to the angularity, grading and density of the particles. Some conservative values of these parameters are set out in Table D2.

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TABLE D2

φ′ FOR SILICEOUS SANDS AND GRAVELS

Angularity (see Note 1) (kA) (degrees)

Rounded 0

Sub-angular 2

Angular 4

Grading of soil (see Note 2 and

Note 3)

(kB) (degrees)

Uniform 0

Moderate grading 2

Well graded 4

N ′ (below 300 mm) (see Note 4) (kC) (degrees)

<10 0

20 2

40 6

60 9

NOTES:

1 Angularity is estimated from visual description of soil.

2 Grading may be determined from grading curve by the use of—

Coefficient of uniformity = D60/D10

where D10 and D60 are particle sizes such that, in the sample, 10% of the

material is finer

than D10 and D60 and 60% us finer than D60.

Grading Uniformity

Uniform

Moderate grading

Well graded

< 2

2 to 6

6

3 A step-graded soil should be treated as uniform or moderately graded soil according

to the grading of the finer fraction.

4 N′ from results of standard penetration test modified where necessary.

5 Intermediate values of kA, kB and kC are given by interpolation.

D2.2.4 Rock materials

The engineering properties of rock, relative to the design of an earth-retaining structure, is

usually controlled by the extent and orientation of bedding planes and joints within the rock

mass, together with any water pressures on discontinuity planes.

Whilst site investigation processes should normally determine the appropriate friction angle

to be adopted, some conservative values of φ′ are set out in Table D3.

D2.2.5 Fill materials

Fills have been classified in this Standard as being Class I or Class II controlled fill,

uncontrolled fill and other fill. Whilst a wide range of fills may be used as backfill behind

retaining walls, selected cohesionless granular fill placed in a controlled manner behind the

wall is usually the most desirable.

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‘Other fill’ should not be used as fill under, within or behind retaining structures unless

specific investigations show that it is suitable; as such, no recommendations for ‘other fill’

are made in the Tables in this Standard.

Where plastic cohesive fills are used behind walls, the same can cause problems during

both the design and the construction phases; this is because of aspects such as shrink/swell

of the clays, softening of the clays with saturation and so on. Consequently, where clays of

higher than low-to-moderate plasticity (viz. a PI of greater than 20) are used, then special

attention should be paid to items such as shrink/swell and softening.

In the case of reinforced soil structures, it is usually necessary to be very specific about the

fill material to be used in the reinforced soil block. Some suggestions on the various types

of fill for reinforced soil structures are provided in subsequent Paragraphs of this Appendix.

TABLE D3

φ′ FOR ROCK

Stratum φ′ (degrees)

Chalk 35

Weathered granite 33

Fresh basalt 37

Weak sandstone 42

Weak siltstone 35

Weak mudstone 28

NOTES:

1 The presence of a preferred orientation of joints, bedding or cleavage in

a direction near that of a possible failure plane may require a reduction

in the above values, especially if the discontinuities are filled with

weaker materials.

2 Chalk is defined here as unweathered medium to hard, rubbly to blocky

chalk.

3 Weathered basalt may have very low values of φ′ .

D3 TYPICAL SOILS

Whilst the variety of soils encountered in practice is very large, the usual range of soils can

be classified as set out in Table D4.

TABLE D4

SOIL CLASSIFICATION

Soil parameters Soil group Typical soils in group

c′ kPa φ′ (degrees)

Poor Soft and firm clay of medium to high plasticity, silty clays,

loose variable clayey fill, loose sandy silts 0 to 5 17 to 25

Average Stiff sandy clays, gravelly clays, compact clayey sands and

sandy silts, compacted clay fill (Class II) 0 to 10 26 to 32

Good Gravelly sands, compacted sands, controlled crushed

sandstone and gravel fills (Class I), dense well-graded sands 0 to 5 32 to 37

Very good Weak weathered rock, controlled fills (Class I) of roadbase,

gravel and recycled concrete 0 to 25 36 to 43

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D4 FILL MATERIALS FOR REINFORCED SOIL STRUCTURES

D4.1 General

Fill materials for reinforced soil structures should be free from any organic, plastic, metal,

rubber or any other synthetic material, inorganic contaminants, dangerous or toxic material

or material susceptible to combustion. Fill materials should consist of naturally occurring or

processed materials that are capable of being compacted in accordance with the specified

requirements, to form a stable mass of fill.

Where reinforced soil structures are used to retain highly plastic or reactive soil materials,

then the impact of the shrink/swell movements of such soils on the reinforced soil

structures, embedded services and associated structures should be considered in the design.

Fill materials should have values of shear strength and soil/reinforcement friction consistent

with the design parameters. The reinforced soils design should specify physical, chemical

and electrochemical properties.

Select or other fill materials may be used for reinforced soil structures as defined in

Paragraphs D4.2.2 and D4.2.3.

D4.2 Select fill for reinforced soil structures

D4.2.1 General

Select fill material for reinforced soil structures should be a frictional, non-aggressive

material of either natural or industrial origin, free of organic material, meeting the physical,

chemical and electrochemical criteria defined in Paragraph D4.2.

The use of select fill material as defined in Paragraphs D4.2.2 and D4.2.3 will allow

appropriate design parameters to be adopted as defined in Paragraphs D4.2.4 and D4.2.5,

provided that it is constructed as defined in Paragraph D4.2.6. This material will result in a

sound, durable structure whose design and construction performance will be predictable

over a wide range of construction and service conditions.

D4.2.2 Physical properties

Select frictional fill material should be defined based on the physical (size) properties of the

fill material in place (after compaction) as follows:

(a) Grading as determined by AS 1289.3.6.3 should be within the limits defined in

Table D5 below:

(b) If more than 15% of the material passes the 75 µm sieve, then not more than 10% of

the material should have a diameter less than 20 µm.

(c) Coefficient of uniformity should be greater than 2.

(d) Plasticity index should be less than 12.

D4.2.3 Chemical and electrochemical properties

Select non-aggressive fill material may be defined based on the chemical and

electrochemical properties described in Table D6.

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TABLE D5

PARTICLE GRADING

Particle size Percent passing

150 mm 100

95 mm 25–100

236 mm 15–100

600 µm 10–100

75 µm 0–15

NOTE: For geosynthetic reinforcement, use of larger

particle sizes may require a decrease in the damage

factor

TABLE D6

BASIC SOIL PROPERTIES FOR NON-AGGRESSIVE SELECTED BACKFILL

Classification S1 S2

Resistivity (ohm, cm) >5000 >1000

pH (min.) >5 >5

pH (polyester, galvanized steel only) <10 <10

Chlorides (mg/kg) — <200

Sulfates (mg/kg) — <1000

D4.2.4 Design parameters, physical

The soil shear strength parameters (required by Section 5), for select fill material as defined

in this Appendix, should be taken as follows:

(a) Characteristic friction angle ........................................................................ φ′ = 36°.

(b) Characteristic drained cohesion ........................................................................c′ = 0.

D4.2.5 Design parameters, chemical and electrochemical

The corrosion allowances defined in Table D7 should be adopted to assess the combined

reduction factors for strength and thickness (required by Section 5), for steel reinforcements

buried in selected fill material.

TABLE D7

CORROSION ALLOWANCES (mm)

Design life (years) 5 30 100

Plain 0.5 1.5 4.0 Land based

Galvanized 0 0.5 1.5

Plain 0.5 2.0 5.0 Freshwater

Galvanized 0 1.0 2.0

Marine Plain 1.0 3.0 7.0

NOTE: The corrosion allowance is the total effective loss of thickness in a

section from which is determined the residual tensile strength.

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D4.2.6 Construction

The select fill in the reinforced soil structure should be placed and compacted in layers of

thickness appropriate to the compaction methods to be used and so that each layer of fill is

completed at the connection to the facing panel.

The select fill placement should closely follow the erection of each course of facing panels

and should be placed and spread in a direction parallel to the face of the structure. Plant

with an equivalent static weight of more than 10 kN should be excluded from a zone

extending to 1.5 m from the facing panels of the structure. Compaction of the select fill in

this zone should be carried out using hand-operated equipment with an equivalent static

weight of less than 10 kN, to achieve the equivalent density to that achieved in the main

body of the reinforced soil structure.

The select fill should meet the requirements of a controlled fill (Class I) and compacted to

provide a uniform density over the full width of the reinforced fill structure.

A minimum of 1 in situ density test to verify compaction should be carried out per layer, as

follows, except in the case of structure classification 3:

(a) For plan areas of filling less than 1000 m2, one test every 200 m

3.

(b) For plan areas of filling greater than 1000 m2, one test every 500 m

3.

D4.3 Other fill for reinforced soil structures

D4.3.1 General

Fill for reinforced soil structures may be outside the criteria for select fill defined in

Paragraph D4.2 provided that the design and construction of the structure takes into account

the performance characteristics of the material, both in the short and long term, and

appropriate controls are provided.

The use of highly plastic or expansive clays is not recommended for reinforced soil

structures, because of the potential for movement due to changes in moisture content.

D4.3.2 Physical properties

The maximum particle size should be limited by the needs of the earthworks placement and

compaction. As a guide, the maximum particle size should be limited to two-thirds the

compacted layer thickness and should be consistent with the design criteria used to take into

account construction damage.

The minimum particle size should be limited by the need to control plasticity and to achieve

consistent shear strength and frictional resistance with the reinforcement under construction

and in-service conditions. A minimum particle size limit of not more than 20% smaller than

20 µm is recommended, with up to 40% smaller than 20 µm being possible, subject to

detailed testing and performance evaluation.

D4.3.3 Chemical and electrochemical properties

The chemical and electrochemical properties of the fill should be appropriate to the material

and the service life of the structure, based on relevant test data.

D4.3.4 Design parameters, physical

The design soil shear strength and the friction coefficient should be assessed based on the

soil fill and the reinforcement material to be used. Fill that exhibits a friction angle (φ) less

than 24° should not be used, and a maximum cohesion value (c) of 5 kPa should be used in

the calculation.

D4.3.5 Design parameters, chemical and electrochemical

Material reduction factors should be based on appropriate test data for the soil and

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D4.3.6 Construction

The placement and compaction of fill in a reinforced soil structure should meet the

recommendations of Paragraph D4.2.6.

The fill should be compacted to provide a uniform density over the full width of the

reinforced soil structure. The minimum density should be consistent with the design of the

soil and the reinforcement, and strength and performance criteria of the structure.

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APPENDIX E

DESIGN MODELS AND METHODS

(Informative)

E1 DESIGN MODELS

There are various methods of calculation of earth pressures on retaining walls and some

methods of calculation are only appropriate in very particular circumstances (for example,

the Rankine theory is only applicable to vertical walls). Further, the effect of the ‘restraint’

conditions on the wall can vary enormously the distribution of the earth pressures behind a

wall.

Therefore, it is very important to select—

(a) the appropriate method analysis; and

(b) the wall restraint conditions.

A guide as to the applicable earth pressure theories is given in Table E1, whilst the various

restraint conditions are illustrated in Figures E1 to E5.

In addition, as an individual earth pressure theory may only inadequately describe the likely

forces on the wall, the designer should consider the degree to which the design model is

applicable to a particular site and include an appropriate ‘partial factor’, if required.

As the analysis of structures that slope backwards at an angle that approximates the typical

‘Coulomb Wedge’ (see Figures E3 and E4) requires a consideration of the overall stability

of the slope using slope stability analysis methods, this Standard does not provide the

recommendations or requirements for the design of this form of structure, which is usually

termed a ‘revetment structure’ (see Figure 1.1).

Where retaining walls using ‘embedded piles’ are adopted at a site, the design of such

structures should be carried out as suggested in AS 2159 for laterally loaded piles.

E2 DESIGN METHODS

E2.1 Safety in design

According to this Standard, safety is incorporated in the design process by the following:

(a) Using conservative soil properties in the analysis of stability, deformation, seepage or

other ground engineering problems. This Standard prescribes or recommends factors

by which characteristic material properties are multiplied in order to lead to a safe

design (Section 5).

(b) Factoring up loads where they contribute to ground failure or excessive deformation,

and factoring down loads that resist failure or reduce deformations (Section 4).

(c) The designer should be aware that additional safety in design may result from—

(i) performing laboratory or field tests that tend to underestimate strength or

overestimate deformation of soils;

(ii) sampling and testing soils with a bias towards finding the most unfavourable;

result;

(iii) using methods of analysis that are known to give conservative results; and

(iv) using empirical correlations that tend to err on the safe side.

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Conversely, safety may be reduced where the above techniques are deemed to yield non-

conservative results.

NOTE: The following alternative design approaches to retaining walls may be used, provided the

same design considerations and performance criteria as outlined in this Standard are satisfied:

(a) For walls other than reinforced soil walls, a global (lumped) geotechnical resistance factor

may be used, rather than partial material design factors. No guidance is given in this

Standard for the choice of global factors.

(b) A safe design of conventional retaining structures can also be achieved by analysing limit

equilibrium conditions using the worst credible soil parameters. A factor of safety just

exceeding 1 would be sufficient to prevent failure. However, if the chosen safety factor is

also intended to limit displacements to a tolerable maximum, the lowest credible soil

strength will need to be further reduced by dividing it by a partial factor. This approach is

referred to as the Direct Assessment (Worst Credible Scenario) method. No guidance for this

approach is given in this Standard.

E2.2 Representative material properties

E2.2.1 General

In this Standard, representative material properties are called characteristic values. The

meaning of characteristic value may vary depending on the particular material involved and

conventions in the relevant industry.

Material design factors (Section 5) are thus applied to characteristic values (Refer

Clause 1.4.1.4).

E2.2.2 Soil shear strength parameters

The Mohr-Coulomb failure criteria contains two parameters, c′ and ,φ′ commonly referred

to as the cohesion and the friction angle respectively, regardless of their true physical

interpretation. Different sets of strength parameters are defined depending on loading and

drainage conditions or the stress-strain characteristics as follows:

(a) Peak values are strength parameters determined from the highest strength value

recorded during the test. Peak values are traditionally used in the analysis of bearing

capacity and the determination of earth pressures.

(b) Effective strength parameters c′ and φ′ as obtained from a drained shear test or an

undrained shear test with pore pressure measurements. These parameters are used for

the analysis of free-draining granular soils and the long-term stability of clays.

(c) Undrained strength parameters cu and φu as obtained from an undrained shear test. These parameters are used for the analysis of short-term stability, or stability under sudden loading of clays.

(d) Ultimate, constant volume or critical values (φcr or φcv) are derived from measurements where the sheared specimen has reached constant volume conditions (usually at a strain of say 10%). These values are used in analyses based on the concept of critical state soil mechanics.

(e) Residual values (φr) are determined at very large strains (say 100%). They may be relevant for the analysis of the global stability of a wall in a slope with a history of instability.

For any analysis involving soil shear strength, an appropriate set of shear strength

parameters has to be chosen.

For retaining structures with controlled backfill, analysis with effective strength parameters

is usually critical. Partial factors given in Section 5 are applied to strength components

based on effective strength parameters.

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For retaining structures supporting excavations in saturated clay and possible for other soil

or loading conditions, undrained analysis may be more critical than an analysis using

effective strength parameters. For some problems, it may be appropriate to analyse both,

undrained and drained (effective stress) conditions. Undrained strength of clays is referred

to in Paragraph D2.2.2 of Appendix D.

E2.3 Notation

For the purpose of this Appendix, the following notation applies:

c = Characteristic cohesion of a soil, which is a parameter in the Mohr-Coulomb

failure criteria, also referred to as the cohesion intercept

c′ = characteristic effective cohesion of a soil

cu = characteristic undrained cohesion of a soil

c* = design cohesion of a soil

φ = characteristic angle of shearing resistance of a soil, which is a parameter in the

Mohr-Coulomb failure criteria, also referred to as the internal friction angle or

simply friction angle

φ′ = characteristic effective internal friction angle of a soil

φu = characteristic undrained internal friction angle resistance of a soil

φcv = critical or constant-volume internal friction angle of a soil under effective stress

conditions

φr = residual internal friction angle of a soil under effective stress conditions

φ* = design internal friction angle of a soil

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FIGURE E1 RANKINE DESIGN MODEL

FIGURE E2 RANKINE-BELL DESIGN MODEL

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FIGURE E3 COULOMB ANALYTICAL DESIGN MODEL

FIGURE E4 GENERAL WEDGE ANALYSIS DESIGN MODEL

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FIGURE E5 EFFECT OF RESTRAINT CONDITIONS ON EARTH PRESSURES Acc

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APPENDIX F

MATERIAL SELECTION AND DURABILITY

(Informative)

F1 GENERAL

The selection of materials for earth-retaining structures should take into account the

characteristics of the material, its durability in the environment and its performance with

time, as defined in Section 3.

F2 REINFORCED SOIL STRUCTURES

F2.1 General

The selection of soil-reinforcing products should take into account the following factors:

(a) Strength characteristics.

(b) Strain behaviour, at ultimate and serviceability limits states.

(c) Soil/structure/reinforcement interaction behaviour.

(d) Handling and construction behaviour.

(e) Durability.

F2.2 Durability

The principal factors that are likely to affect the durability of soil reinforcement are as

follows:

(a) General factors:

(i) Loading (metallic and polymeric).

(ii) Water (metallic and polymeric).

(iii) Damage (metallic and polymeric).

(iv) UV exposure (polymeric).

(v) Temperature (polymeric).

(b) Specific factors:

(i) Bacterial (metallic and polymeric).

(ii) Chemical (metallic and polymeric).

(iii) Electrochemical (metallic).

(iv) Corrosive fluids (metallic).

(v) Aggressive fluids (polymeric).

A check list of factors that should be considered for the selection of soil-reinforcing

products is given in Table F1.

F3 REINFORCED SOIL AND RETAINING STRUCTURES

The selection of materials for use in all earth-retaining structures should take into account

the factors identified in Table F2.

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TABLE F1

CHECK LIST FOR INVESTIGATIONS OF SOIL-REINFORCEMENT PRODUCTS

(a) Physical and mechanical properties:

(i) Full description of the material and relevant technical literature.

(ii) Short- and long-term data: ultimate and permissible values of tensile strength; stress strain

curves; value of Young’s modulus; creep; pliability, ductability; fatigue (dynamic and static)

however induced, e.g. structural, thermal or tidal loading; coefficient of friction with fill (with

no protective coating)

(b) Durability:

The effects of the following agencies on physical and mechanical properties to be investigated:

Extreme pH values; chlorides; sulfates; ozone; hydrocarbons and other chemicals common on

transport highways; water; ultraviolet and infra-red rays (including short-term exposure prior to

installation); bacteria and other animal and vegetable life forms; fire; vandalism

(c) Performance during installation and use:

(i)

(ii)

(iii)

(iv)

Handling, storage

Damage

Extension and movement

Effects on facing

during deposition, spreading and

compacting of fill in structure and

under test loading

These topics to be checked by site trial(s)

(d) The effect of the combination of load, chemical environment and construction damage, i.e.

combination of Items (a), (b) and (c)

(e) Constructional details:

Connections: effect on Items (a)(ii) and (b)

(f) Quality control procedures and problems associated with production processes

(g) Preconstruction exposure to an aggressive environment, e.g. long-term effect of short-term UV

exposure on synthetics, or ozone and marine spray on metallics

(h) The effects of static fatigue (creep) or dynamic fatigue however induced; e.g. structural loading,

thermal loading, creep ratcheting

(i) The effects of blasts, fires or vandalism on the behaviour of the structure

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TABLE F2

FACTORS AFFECTING THE DURABILITY AND PERFORMANCE OF

EARTH-RETAINING STRUCTURES

Retaining wall elements Factors affecting durability

Concrete/masonry Loading

Weathering

Temperature (including freeze/thaw)

Permeability to air/moisture

Chloride attachment (marine environment)

Composition of soil (acids/sulfates)

Concrete quality (mix design, compaction and the like)

Concrete strength (cement content)

Corrosive liquids and gases

Sulfate attack (seawater, ground water, industrial effluent)

Steel reinforcement (in concrete structures) Loading

Concrete quality (mix design, compaction and the like)

Concrete permeability

Aggressive salts (chlorides and sulfates)

Concrete cover to steel

Climate (temperature, humidity, rainfall and the like)

Timber Loading

Termites (white ant)

Borers

Moisture (causing swelling/splitting)

Weathering (sunlight and rain causing ‘silvering’)

Decay or fungal deterioration (also called ‘rot’)

Fire

Composition of timber (namely, the presence of resins

that affect durability)

Metallic soil reinforcement Loading

Water

Damage (especially to galvanized/sacrificial coatings)

Temperature

Electrochemical properties of soil

Composition of soil (acids, chlorides, sulfates, sulfides,

organic content)

Chloride attack (marine environment)

Sulfate attack (seawater, ground water, industrial effluent)

Corrosive liquids and gases

High density polyethylene soil

reinforcement

Loading

Damage

UV exposure (pre-use)

Temperature

Aromatic/aliphatic hydrocarbons

Halogenated hydrocarbons

Polyester soil reinforcement Loading

Temperature

Water (hydrolysis)

Water absorption properties of the polyester

Permeability and durability of type of outer protective

coating (usually polyethylene)

Damage (especially of outer protective coating)


Polypropylene soil reinforcement Loading

Damage


Temperature

Aromatic/aliphatic hydrocarbons

Halogenated hydrocarbons

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APPENDIX G

DRAINAGE OF EARTH-RETAINING STRUCTURES

(Informative)

G1 GENERAL

As drainage is perhaps the most important consideration in the design of earth-retaining

structures, it is very important that the drainage systems are carefully designed and

specified with sufficient detail to ensure that the system can be correctly constructed.

Water may affect a structure in the following ways:

(a) Percolation from the upper surface.

(b) Groundwater or seepage flow from the retained ground.

The drainage system needs to cater for both situations. It is also important to separate the

surface drainage system from the subsoil drainage system to ensure the long life of the

subsoil system. This is usually achieved by a 300 to 500 mm thick layer of compacted clay

or sandy clay material placed over the subsoil system to act as a seal. Also, prevention of

ponding of surface water behind the top of the wall is important.

Whilst this Appendix includes details of various methods of providing subsoil drainage

relief behind retaining structures, it is very important that the designer of the wall consider

carefully the operation of the subsoil and surface drainage system and produce a ‘site

specific’ design.

G2 DRAINAGE MATERIALS

G2.1 Backfill materials

The backfill material for an earth-retaining structure needs to be carefully considered and

specified. In this regard, careful attention should be paid to the permeability of the material,

ease of compaction and availability. Further, ‘soil filter’ requirements to prevent the

migration of fine particles into the more open-graded filter material should be considered.

Because of the difficulty in matching available filter materials with permeability and

particle migration requirements, it is usual practice to incorporate a geotextile to separate

the filter material from the in situ materials. Such geotextiles need, however, to be selected

with care and specified in terms of material type, branch, permeability and function.

Subsoil drainage and filters must also be properly designed in accordance with recognized

filter design criteria, to prevent piping as well as satisfying permeability requirements.

In timber or concrete crib walls, it is sometimes assumed that the infill material within the

crib units acts as a sufficient drainage medium; however, experience has indicated that the

usual crib infill material often lacks sufficient permeability when compacted. Further, if a

sufficiently permeable crib infill is used, then there are usually problems with the material

behind the crib wall; thus, both the backfill and infill material need to be carefully specified

for a crib-type wall.

G2.2 Geosynthetic materials

Where geosynthetic materials are used (e.g. geotextiles and geocomposite drains) careful

consideration should be given to the permeability and surface tension properties of the

geotextile. This is because some materials are in fact water repellent until they are fully

saturated and the surface tension effect removed. Should a geotextile material with a high

surface tension (i.e. the geotextile is ‘hydrophobic’) be used, then low seepage flows will

seek to move through the drainage system in a manner not intended by the designer. Such a

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situation can have very serious effects on the foundation materials on which the structure is

built, as well as causing subsoil water effluxes in inappropriate locations.

Further, where the subsoil system is subject to high lateral pressures (e.g. wall in excess of

4 m), crushing of geocomposites and subsoil drainage pipes can occur if they are not

designed to resist these pressures.

G3 PIPEWORK AND MAINTENANCE

G3.1 Pipework

The design drawings should clearly indicate the specific location of the various pipes

required (including size, class, type and joining method) and all pipework should be

provided with adequate falls to ensure free flow of the drainage pipes. In this regard

attention is drawn to AS 3500 and AS 2439.

In addition, it is desirable that the design provides for—

(a) testing and cleansing of the installation (e.g. flushing points): and

(b) appropriate tolerance on the laying of pipes.

Where feasible, it is also preferable to provide weepholes in addition to any subsoil

drainage system.

G3.2 Maintenance and clogging of drainage systems

In addition to the durability of the drainage material used in a particular application, the

potential for clogging of the drainage system due to migration of fines, or the formation of

iron oxide from the soil/ground water system, should be investigated. Experience has also

indicated that some geotextile materials ‘clog up’ with time if a suitable sand filter

(approximately 50 mm thick) is not placed between the geotextile and the in situ material.

Thus, it is important to either provide for this extra filter layer, or design the geotextile on

the basis that some long-term clogging takes place.

Where it is considered inevitable that some long-term clogging will take place, then the

reduced effectiveness of the subsoil drainage should be included in the design calculations.

In the case of potential formation of iron oxide, special measures may also be incorporated

in the design to allow for clearing of iron oxide blockage by flushing with suitable organic

acids.

Whilst subsoil drainage systems are normally designed so that maintenance is not required,

there may be some instance where maintenance is part of the design specification. In such

cases, the requirements of Section 8 need to be carefully considered. It should be

recognized, however, that in the majority of cases, the specified maintenance may not be

done and, therefore, it is usually prudent to adopt a more conservative design (that is,

failure or partial failure of drainage system) rather than to assume the maintenance has been

carried out.

G4 TYPICAL DRAINAGE DETAILS

Typical details of reinforced soil structures (RSS) are shown in Figure G1.

The design requirements of an RSS are such that the reinforced soil zone is usually more

permeable than the material behind the RSS structure and, thus, the reinforced soil mass can

be effective as a drain without additional requirements, in some cases. However, before

adopting this method of drainage, consideration should be given to—

(a) leaky services within the RSS structure; and

(b) ground water rise after RSS construction.

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Where there is a requirement to divert seepage and run-off from the side (excavated) slope

behind the RSS, the details shown in Figure G2 are more appropriate. Several methods are

used to intercept and divert the seepage water away, as follows:

(i) A longitudinal subsoil pipe installed in a trench at the toe of the RSS either in front of

the wall facing or immediately behind the facing.

NOTES:

1 Where the drain is laid in front of the wall facing, weepholes are normally required in

selected panels.

2 Subsoil pipes should be sufficiently rigid and durable. The collected water should also be

connected into the stormwater drainage system with a suitable ‘non-return’ protection

system.

(ii) Blanket drains may be laid either under or behind the RSS in cases where medium to

high water seepage conditions are anticipated. Alternatively, trench drains at regular

intervals may be used along the length of the structures.

Where blanket drains are used, they are typically 200 to 300 mm thick. Such drains

use a free-draining gravel material, encapsulated in a suitable geotextile.

G5 TYPICAL DRAINAGE DETAILS—EARTH-RETAINING STRUCTURES

Unless the retaining wall is designed to resist both hydrostatic and earth pressures, a

suitable subsoil drainage system should be incorporated into the structure design.

Where required, blanket drains may be laid either immediately behind the structure or at the

interface between the natural ground and the retained backfill. Alternatively, geocomposite

drainage products may be used in cases where the imposed overburden stresses do not

damage or crush the geocomposite materials. It is also usual to adopt a combination of

natural and geosynthetic materials, depending on the site conditions and construction

limitations.

Figures G3 to G8 show a number of typical details for various types of wall structures;

however, these details will need to be specifically modified for a particular situation.

The details do not provide the overall drainage plan required as part of the subsoil drain

design. In this regard, in addition to the typical sections shown, it is necessary to provide a

plan of the drainage works illustrating both the efflux points for the drainage and access and

maintenance points (e.g. flushing points).

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FIGURE G1 TYPICAL SECTION FOR REINFORCED SOIL STRUCTURES—DRAINAGE

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G6 SOIL NAIL STRUCTURES

The drainage of soil nail structures is extremely important to their long-term successful

performance. As such structures are usually formed by the installation of tensile elements

into natural soil or weathered rock materials, drainage techniques typically involve the

drilling of a number of subhorizontal boreholes into the in situ material and the providing of

relief drainage at the surface of the soil nail structure.

Additionally, as there is sprayed concrete facing applied to the surface of the in situ

material, regular weepholes in the sprayed concrete will be required, or a geocomposite

drainage system will need to be installed between the excavated face of the in situ material

and the sprayed concrete. Should a geocomposite system be used, then it is very important

to ensure a proper hydraulic connection between each section of the geocomposite during

the installation process.

Whilst weepholes at regular vertical and horizontal spacings are often used in conjunction

with a short length of perforated pipe wrapped in geotextile through the sprayed concrete

layer, such a method has been shown by experience to be aesthetically poor and, thus, the

alternative of a geocomposite drain behind the sprayed concrete is usually preferred.

In addition, where significant seepage occurs within and behind the reinforced soil zone,

deeper horizontal drainage systems should be used. In such cases, it is very important to

ensure that the deeper drainage pipes do not act as a ‘focus’ for localized soil piping and

thus possibly contribute to a long-term failure. In this regard, it is usual to wrap the deep

subsoil pipe in a suitable geotextile prior to installation.

FIGURE G3 TYPICAL SECTION—CANTILEVERED WALL DRAINAGE, TYPE 1

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FIGURE G4 TYPICAL SECTION—CANTILEVERED WALL DRAINAGE, TYPE 2

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FIGURE G5 TYPICAL SECTION—CRIB WALL DRAINAGE

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FIGURE G6 TYPICAL SECTION—GRAVITY BOULDER WALL DRAINAGE

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FIGURE G7 TYPICAL SECTION—GABION WALL DRAINAGE

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FIGURE G8 TYPICAL SECTION—POST-AND-LOG WALL DRAINAGE

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APPENDIX H

REINFORCED SOIL FACING SYSTEM CONNECTION LOADS

(Informative)

H1 DESIGN LOAD

The design load at the connection between the facing elements and the soil reinforcement of

a reinforced soil structure should be between 75% and 100% of the maximum load

determined for the soil reinforcement in the structure, depending on the design model

appropriate to the soil reinforcement stiffness and the facing system flexibility.

H2 COHERENT GRAVITY METHOD

For inextensible reinforced structures designed using the ‘coherent gravity’ method, the

ratio of the design load at the reinforcement facing connection Tcj* to the design maximum

tensile force in the jth

layer Tj* may be taken as indicated in Table H1.

TABLE H1

CONNECTION LOADS—COHERENT GRAVITY METHOD

Location

Facing system From the top of

structure to a depth of

0.6H, percent

At base of

structure, percent

Flexible face (e.g. curved metal sheets) 75 100

Articulated panels with flexible joints (e.g. precast

concrete panels with >1% joint compression capacity) 85 100

Vertically stiff walls or walls with no vertical

movement capacity (e.g. full height panels, modular

block walls)

100 100

NOTE: Values may be linearly interpolated at other locations.

H3 TIE-BACK WEDGE METHOD

For extensible reinforced structures designed using the ‘tie back wedge’ method, the ratio

of the design load at the reinforcement facing connection Tcj* to the design maximum

tensile force in the jth

layer Tj* may be taken as indicated in Table H2.

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TABLE H2

CONNECTION LOADS—TIE-BACK WEDGE METHOD

Location

Facing system At top of structure,

percent

At base of structure,

percent

Flexible face (e.g. curved metal sheets, geotextile wrap

around) 75 100

Articulated panel with flexible joints (e.g. precast concrete

panels with >1% joint compression capacity) 75 100

Vertically stiff walls or walls with no vertical movement

capacity (e.g. full height panels, modular block walls) 100 100

NOTE: Values may be linearly interpolated at other locations.

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APPENDIX I

EARTHQUAKE DESIGN

(Normative)

I1 GENERAL

This Appendix provides design requirements for the following:

(a) Situations where earthquake loading requirements are deemed to be met by static

design for factored dead and live loads (including soil pressure and surcharges).

(b) The calculation of earthquake loads.

NOTE: The approach is generally consistent with that of AS 1170.4 (which is applicable to

building design), except where modifications have been made to account for the differences

between the behaviour of buildings and earth-retaining structures.

I2 PROCEDURE

The following steps shall be carried out:

(a) Determine the structure classification.

(b) Determine the acceleration coefficient for the particular location.

(c) Determine the soil profile and site factor relating the soil profile to the acceleration of

the structure and retained soil.

(d) Determine the earthquake design category.

(e) Execute the required design method.

Where detailed analysis and design for earthquake loads are required, these shall be carried

out in accordance with Paragraph I8.

I3 STRUCTURE CLASSIFICATION

The structure classification shall be determined in accordance with Clause 1.2.2 and

Table 1.1.

NOTE: Clause 1.2.2 and Table 1.1 are based on assessment of the risk to life, and Appendix A

gives further guidance on the determination of that risk, taking into account height of the

structure, proximity to other structures and type of facing and cladding.

I4 ACCELERATION COEFFICIENT

The acceleration coefficient (a) shall be determined in accordance with AS 1170.4.

NOTE: Acceleration coefficient is related to the expected severity of earthquake ground motion

before taking account of local site conditions. AS 1170.4 sets out maps showing the distribution

of acceleration coefficients throughout Australia. Table H1, reproduced from AS 1170.4, provides

the acceleration coefficient at the principal cities.

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TABLE I1

ACCELERATION COEFFICIENT FOR

MAJOR CENTRES

Major centres Acceleration coefficient (a)

Adelaide 0.10

Albury/Wodonga 0.08

Ballarat 0.08

Bendigo 0.09

Brisbane 0.06

Cairns 0.06

Canberra 0.08

Darwin 0.08

Geelong 0.10

Gold Coast/Tweed Heads 0.06

Hobart 0.05

Latrobe Valley 0.10

Launceston 0.06

Melbourne 0.08

Newcastle 0.11

Perth 0.09

Rockhampton 0.08

Sydney 0.08

Toowoomba 0.06

Townsville 0.07

Wollongong 0.08

I5 SOIL PROFILE AND SITE FACTOR

The site factor (S) shall be determined in accordance with Table I2 for the appropriate soil

profile. Interpolation for soil profiles in between those given in Table I2 is permitted. For

structures classification C in accordance with Table 1.1, the soil profile should be

established from substantiated geotechnical data and classified in accordance with AS 1726.

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TABLE I2

SITE FACTORS FOR GENERAL STRUCTURES

Soil profile below the structure Site factor (S)

A profile of rock materials with rock strength Class L (low) or

better 0.67

A soil profile with either—

(a) rock materials Class EL (extreme low) or VL (very low)

characterized by shear wave velocities greater than

760 m/s; or

(b) not more than 30 m of—

(i) medium dense to very dense coarse sands and

gravels;

(ii) firm, stiff or hard clays; or

(iii) controlled fill.

1.0

A soil profile with more than 30 m of—

(a) medium dense to very dense coarse sands and gravels;

(b) firm, stiff or hard clays; or

(c) controlled fill.

1.25

A soil profile with a total depth of 20 m or more and containing 6

to 12 m of—

(a) very soft to soft clays;

(b) very loose or loose sand;

(c) silts; or

(d) uncontrolled fill.

1.5

A soil profile with more than 12 m of—

(a) very soft to soft clays;

(b) very loose or loose sands;

(c) silts; or

(d) uncontrolled fill,

characterized by shear wave velocities less than 150 m/s

2.0

NOTES:

1 For the purposes of this Standard, it is not intended that a detailed site investigation be

carried out for any structure to determine a soil profile over large depths. Most major

centres and regional areas have basic information available on the likely strata that

should be used to assess the site factor (S)

2 Small variations such as isolated layers within the overall profile not exceeding 2 m

average depth or changes at or near the surface not exceeding 3 m average depth need not

be considered.

I6 EARTHQUAKE DESIGN CATEGORY

The earthquake design category shall be determined from Table I3 for the appropriate value

of the product of acceleration coefficient and site factor (aS) and the structure

classification.

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TABLE I3

EARTHQUAKE DESIGN CATEGORY

Design category

Structure classification

Product of acceleration

coefficient and site factor

(aS)

C B A

aS ≥ 0.2 Eer

Der

Cer

0.1 ≤ aS < 0.2 Der

Cer

Ber

aS < 0.1 Cer

Ber

Aer

I7 DESIGN REQUIREMENTS

Earth-retaining structures shall be designed as set out in Table I4, depending on the

earthquake design category.

TABLE I4

DESIGN REQUIREMENTS

Earthquake design

category Design requirements

Aer

Design for static loads, without further specific analysis for earthquake, is

deemed to meet the requirements of this Standard for earthquake design

Ber

Design for static loads, without further specific analysis for earthquake, is


Cer

Design for static loads, with a dead load factor of 1.5 (in lieu of 1.25), is


Der

Analysis and design for earthquake loading, as set out below, is required

in addition to design for static loads

Eer

Analysis and design for earthquake loading, as set out below, is required

in addition to design for static loads

I8 SPECIFIC EARTHQUAKE ANALYSIS AND DESIGN REQUIREMENTS

Where detailed analysis and design for earthquake loads are required, these shall be carried

out.

Factors that need to be considered in the design of retaining structures for earthquake

loading include the following:

(a) Ground acceleration.

(b) Acceleration of the structure and retained soil.

(c) External dynamic earth pressure load on the structures.

(d) Dynamic load of the structure itself.

(e) Internal dynamic load (active zone mobilization in reinforced soil).

(f) Internal and external stability criteria.

(g) Safety factors.

(h) Load combinations.

(i) Deformations.

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I9 GROUND ACCELERATION

The ground motion experienced at a particular site due to an earthquake is dependent on

many factors including the following:

(a) Earthquake magnitude.

(b) Source mechanism.

(c) Geological conditions and characteristics of the wave transmission from the source to

the site.

(d) Epicentral distance.

(e) The geology underlying the site soils.

(f) Local characteristics of site soils.

The ground acceleration adopted for design is based on a consideration of the above factors

and would ideally include an assessment of seismicity at the particular site together with

determination of the accepted probability of occurrence (or recurrence interval). For the

determination of ground motion. The following definitions are common:

(i) Maximum design earthquake (MDE).

(ii) Operating basis earthquake (OBE).

I10 MAXIMUM DESIGN EARTHQUAKE (MDE)

The MDE is usually determined from a statistical assessment, which defines the ground

acceleration likely to occur at a long recurrence interval of typically 100 000 years or

longer.

The MDE may be used where major loss of life is possible and, although significant damage

to the structure may be acceptable, complete failure should not occur. That is, a check for

the MDE should ensure that catastrophic collapse does not occur.

I11 OPERATING BASIS EARTHQUAKE

The OBE is considered a normal design case, which should result in minimal damage

occurring to the structure, which should remain in a serviceable condition.

The OBE is based on recurrence interval typical of the design life of the structure (e.g.

50 to 100 years).

For the design of routine structures, it would be usual to adopt the OBE acceleration for

pseudo-static analysis. For most retaining walls, the pseudo-static acceleration is typically

0.5 times the peak ground acceleration (Elms and Martin, Ref. 1) and, although based on

several simplified examples, would be adequate for most design purposes, provided that

allowance is made for an outward displacement of the wall (in millimetres) of the order of

250 times the peak ground acceleration (units of g). In the absence of site-specific data or

particular assessment of seismicity, the peak horizontal ground acceleration can be taken as

the acceleration coefficient (a) from AS 1170.4 times g, recognizing that this has a 10%

chance of exceedence in 50 years, or a recurrence interval of 475 years. This acceleration is

considered representative of motions in rock at depth.

I12 SOIL PROFILE AND AMPLIFICATION

Amplification of seismic activity due to specific site conditions is an area of continuing

research. The following provides some information on potential effects, but each site should

be carefully assessed if site amplification is suspected.

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The peak ground acceleration at a site is dependent on the nature of the subsoils, the

characteristic site period and the period of the base rock excitation. Where soft clay

deposits overlie stiffer materials, significant amplification may occur. In the case of soft to

firm clay sites or for cohesionless soil sites at shallower depth, lower ground accelerations

(say <0.1 g) may be amplified with respect to the peak ground acceleration for rock sites,

whereas for very high ground accelerations (say >0.3 g) soft clays may attenuate maximum

ground accelerations as shear stresses approach the material shear strength and high energy

dissipation occurs (Martin, Ref. 2). For rock, stiff soil and deep cohesionless soil sites there

is unlikely to be any significant influence of soil conditions on peak acceleration values.

The site factor (S) in Table I2 (which is consistent with AS 1170.4) may not be appropriate

to determine the maximum ground acceleration, as this factor applies to the amplification

experienced by framed buildings as a function of foundation conditions, with those

structures whose natural period of vibration closely matches the characteristic period of the

site being most affected.

A specific site assessment may be necessary for soft clay sites. Martin, (Ref. 2) has cited

measured accelerations at the top of 35 to 40 m of soft clay lake-bed deposits of up to

6 times the peak horizontal accelerations of incoming rock motions at depth due to

amplification.

Whilst it would be ideal for a site-specific seismicity assessment to be carried out for

individual sites, this will rarely be warranted and probably only for significant, sensitive or

high hazard structures. Care should be taken with soft soil foundations, where it may be

necessary to determine amplification of rock mass motions relevant for design. Designers

should refer to the current literature or seek specialist advice for such cases.

I13 ACCELERATION OF THE STRUCTURE AND ITS RETAINED SOIL

Traditionally, retaining wall design has been based on pseudo-static methods with zero

vertical acceleration and zero amplification within the structure. In the design of

freestanding walls, it is usual to assume that the wall/soil system has a short fundamental

period of vibration and that the inertia loads correspond to the peak ground accelerations.

Recent work has indicated that, in some cases, amplification of motion in the backfill can

play an important role in displacement estimates. In addition the simultaneous application

of vertical acceleration in the critical direction can increase the earthquake forces. For

pseudo-static analysis such as the Mononobe-Okabe method (Ref. 3) discussed in

Paragraph I14, acceleration coefficients are defined as follows:

(a) Horizontal coefficient of acceleration:

ah = 0.5a

where

a = peak ground acceleration coefficient for deep rock motions from

AS 1170.4

(b) Vertical coefficient of acceleration:

(i) av may vary from 0.3 to >1.0 times ah. Due to the uncertainty of phase and

direction of av with respect to ah, av is often adopted as zero.

(ii) ah and av may require amplification in soft clays and shallow granular layers as

discussed in Paragraph I12. Where adopted, the coefficient av should be applied

in the most adverse direction in determining applied stresses.

(iii) ah is taken as positive acting outwards from the wall.

(iv) av is taken as positive acting upwards.

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Dynamic numerical analysis for reinforced soil walls with metallic reinforcement and

granular backfill have indicated amplification of motions within both the structure

and the retained soil. For these structures, amplification may be assessed as follows:

(i) amh = (1.45 − ah)ah for ah <0.45 . . . I13(1)

= ah for ah ≥0.45

(ii) amv = (1.45 − av)av for av <0.45 . . . I13(2)

= av for av ≥0.45

where amh and amv are the average amplified horizontal and vertical acceleration

within the structure/retained soil.

Design values of acceleration coefficients (defined as kh and kv) have to be taken as ah, amh

and av, amv as appropriate. Although the above amplification has been developed for a

particular wall type, it may be useful as a first approximation for other forms of

reinforcement and other retaining structures in the absence of other information. Dynamic

finite element analyses (Nadim and Whitman, Ref. 4) have also indicated that amplification

of movements in backfill to conventional gravity walls can increase the design acceleration

by 25–50% if motions occur at or near the fundamental frequency of the backfill.

I14 EXTERNAL DYNAMIC EARTH PRESSURE LOAD ON STRUCTURE

Seismic coefficients, kh and kv, are defined in order to calculate both external dynamic earth

pressure and internal dynamic structure load. The seismic coefficients are related to the

average maximum acceleration in the structure as follows:

kh = (amh/g) . . . I14(1)

kv = (amv/g) . . . I14(2)

where amplification in the structure is not considered relevant.

kh = (ah/g) . . . I14(3)

kv = (av/g) . . . I14(4)

The kh and kv values may be halved in accordance with Paragraph I2, provided wall

movement is estimated and checked against acceptable movements for the structures.

For structures in which the use of the coefficient of active earth pressure is appropriate, the

external dynamic earth pressure load (Eac) may be calculated according to the classic

formula of Mononobe-Okabe (Ref. 3) as follows:

Eac = (1/2)γH2∆Kac . . . I14(5)

where ∆Kac = [(1 − kv)Kac] − Ka . . . I14(6)

and Kac is the total active earth pressure coefficient (including seismic effects), Ka is the

static active earth pressure coefficient and ∆Kac is the incremental increase in active earth

pressure coefficient.

The calculation of the total active earth pressure coefficient, (Kac) for cohesionless soils and

a vertical wall (interior face), as proposed by Mononobe-Okabe (Ref. 3), is as follows:

( )

( ) ( ) ( )( )

2

2

ac

coscos

sinsin1cos cos

cos

+−−+++

−=

i

i

K

θδθφδφθδθ

θφ

. . . I14(6)

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where

φ = angle of internal friction of the soil

θ = arc tan[kh /(1 − kv)]

δ = angle of friction between soil and structure

i = backfill slope angle

Limitations on the magnitude of the above parameters apply as documented in the

reference.

The point of application of the total active force is dependent on a number of factors and

can typically be applied at 0.4 H to 0.55 H from the base of the wall (where H is the height

of retained fill) and at the angle δ to the horizontal.

I15 DYNAMIC LOAD OF STRUCTURE ITSELF

The inertia force (Ei) should be calculated from the total weight of the structure, and

superstructure, if appropriate, (W), and the seismic coefficient, as follows:

Eiv = kvW . . . I15(1)

and

Eih = khW . . . I15(2)

The inertia forces for the structure should be applied through the centre of gravity of the

structure.

For larger structures such as reinforced earth walls, it is common to take 0.5 of the wall

inertia effects in recognition of the likelihood that acceleration of the backfill and the wall

may not be exactly in phase.

I16 DYNAMIC WATER PRESSURE

The increase in pore water pressures from earthquake inertia effects should be considered

when soils are below the watertable or structures are inundated (e.g. wharfs or quays). It

should also be noted that by far the most significant source of earthquake-induced damage

to port and harbour facilities has been the pore pressure build up in loose to medium dense

saturated cohesionless backfills. Damage results as a consequence of excessive backfill

pressures and foundation liquefaction.

For the design of permanently inundated structures and backfill several effects or

components of loading (in excess of static conditions) have to be assessed, as follows:

(a) Potential for liquefaction of backfill.

(b) Decreased water pressures outside the structure (if inundated).

(c) Dynamic water pressures in the backfill.

Liquefaction of the backfill is generally not critical for well compacted clay fills or granular

fills at about 65% relative density or higher. Wall foundations may be assessed for

liquefaction using conventional methods based on a standard penetration test (SPT) or cone

penetrometer testing (CPT) data. This will be of greatest significance for structures founded

on loose saturated sands where foundation deformation and instability may control the

design.

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For inundated structures, the reduced restoration effect from the outward displacement of

the impounded water can be of significance. Hydrodynamic pressures from the free water in

front of a wall may be calculated using Westergard’s approximate solution for a vertical

wall and a semi-infinite water reservoir (Ref. 5). The resultant dynamic water pressure

tending to reduce the static water pressure is approximately—

Pwd = (7/12)khγw(Hw)2 . . . I16(1)

applied at 0.4Hw above the base of the wall,

where

γw = density of water

Hw = height of water in front of wall

To determine the effect of variations such as an inclined wall surface and reservoir

geometry, Matsuzawa et al (Ref. 7) provides relevant information. It should be noted that

walls that are normally dry but are subject to flooding are highly unlikely to experience a

simultaneous seismic event and, therefore, this design case is not considered relevant. For

permanently submerged structures, the critical case for overall stability will occur when the

hydrodynamic water pressure reduces the static water pressure in front of the wall and is in

phase with the earthquake earth pressure increment on the wall.

Hydrodynamic water pressures can also develop within saturated backfilled materials. In

the case of highly permeable granular backfills, it can be assumed that the pore water can

move freely in the voids without any restriction from the soil particles. For free-draining

saturated backfills, the calculation of pressures applied to the rear of the wall are

determined in accordance with the recommendations of Matsuzawa et al (Ref. 6), as

follows:

(a) A modified apparent angle of seismic coefficient for use in the Mononobe-Okabe

formula θ ′ is calculated as—

tanθ ′ = Gs/(Gs − 1)tanθ . . . I16(2)

where Gs is the specific gravity of the soil—

θ = tan−1

[kh/(1 ± kv)]

For Gs = 2.65 (typically), tan ≈′θ 6tanθ.

θ ′ is used in the lieu of θ in the equation for Kac.

(b) Static earth pressures are calculated using the buoyant density for zones below the

water table.

(c) Dynamic earth pressure increment is calculated using the buoyant density and θ ′ as

in Paragraph I4.

(d) Static water pressures are calculated as normal.

(e) Dynamic water pressures are calculated using Westergard’s method (Ref. 6) and are

additional to the static water pressures.

(f) The thrust on the wall is the summation of each component.

Matsuzawa et al (Ref. 7) provide more detailed information on assessing the effect of

ground motion on a variety of backfill materials. Whilst the topic is a continuing subject of

research, the approach illustrated here provides a basis for assessing the critical effect of

pore water on seismic response, and may be used in the absence of site-specific

measurements, previous data, or known site performance.

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I17 TOTAL LOAD UNDER EARTHQUAKE

The total load is calculated by adding the static loads and the external dynamic earth

pressure loads, the dynamic water pressure loads, plus internal dynamic loads of the

structure itself.

Normally the loads should be taken in full; however, where appropriate, the use of a

reduced seismic coefficient (as defined in Paragraph I12) or the use of a reduced external

dynamic earth pressure load (usually 50%) may be adopted in accordance with commonly

adopted practice for reinforced soil structures.

I18 INTERNAL DYNAMIC LOAD

The internal stability of a retaining structure should take into account the dynamic load

mobilized by the active zone where it is appropriate for the design of the particular

structural system. This may be a Coulomb wedge on the stem of a cantilever retaining wall

or the active zone of a reinforced soil system.

For a reinforced soil structure, the internal dynamic load from the mobilized active zone is

resisted by the reinforcement layers in proportion to their available frictional resistance.

The internal dynamic load is not considered to act concurrently with the external dynamic

load.

I19 STABILITY AND STRENGTH CRITERIA

The stability criteria will depend on the design approach to be adopted (see Paragraph I12).

In traditional working stress design methods using acceleration coefficients for OBE

analysis, there is no allowance for reduced safety factors and, thus, in the limit state method

all partial factors and load factors would apply. Reduced accelerations may be used in

accordance with Paragraph I2, provided that structure deformations are acceptable.

For MDE analysis, it is usual in a working stress approach to accept an overall factor of

safety of greater than 1 for such a rare event. This may be checked in the limit state

approach by ensuring that the force inequality is satisfied for the serviceability limit state. It

would be acceptable to allow structural strength to approach yield conditions, provided that

brittle or progressive failure is avoided.

I20 APPLIED LOADS

I20.1 General

The load combination for earthquake design ultimate limit state condition should follow the

requirements given in Table J1 of Appendix J, using load case C.

Where traffic load or other live load is carried directly by the retaining structure, the partial

factors for live load (i.e. γq1, γq2) should be taken as 0.5.

I20.2 Effect of superstructure loads

Where retaining structures support each fill (e.g. sloping batter above the structure) the

inertial earthquake force generated by the overlying fill should be calculated in accordance

with Paragraphs I15 and I17.

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For reinforced soil structures supporting bridge abutments, the following is recommended.

(a) The reinforced soil structure should be designed for the factored design earthquake

forces (including factored dead loads) transmitted from the bridge superstructure.

Estimates of the dynamic load are to be provided by the bridge designer. These

dynamic loads should be treated in conjunction with load combinations given in

Paragraph I20.1; however, only 50% of the factored live loads (both vertical and

horizontal) from the bridge superstructure transmitted through the still beam is

required to be included in the analysis.

(b) The additional inertial earthquake force of the sill beam should be included. A

reduced dynamic earth pressure of 50% is permitted for fill retained by the sill beam.

I21 DEFORMATIONS

Relatively large earthquakes (i.e. peak ground acceleration greater than 0.3g) could result in

significant permanent deformation. The likelihood of such movement and its potential

magnitude may be determined by reference to procedures presented by Wood and Elms

(Ref. 8).

I22 REFERENCES

1 ELMS, D.G, and MARTIN, G.R., Factors Involved in the Seismic Design of Bridge

Abutments, Proceedings Workshops on Earthquake Resistance of Highway Bridges,

Applied Technology Council, California, 1979.

2 MARTIN, G.R., Geotechnical Aspects of Earthquake Engineering. State-of-the-Art

Report No. 2, 5th

ANZ Geomechanics Conference, 22-26 August, Sydney, 1988,

(published in Australian Geomechanics Special Issue).

3 MONONOBE, N., Consideration into earthquake vibrations and vibration theories,

J. Japan, Soc. Civ. Engng, 10 No. 5, 1924, 1063-1094.

4 NADIM, F. and WHITMAN, R.V., Seismically Induced Movement of Retaining

Walls. ASCE Journal of Geotechnical Engineering, Vol. 109, No. 7, 1983,

pp. 935-936.

5 OKABE, S., (1924), General theory on earth pressure and seismic stability of

retaining wall and dam, J. Japan. Soc. Civ. Engng 10, No. 5, 1277-1323.

6 WESTERGARD, H.M., Water Pressures on Dams During Earthquake, Transactions

of ASCE, Vol. 98, 1933, pp. 458-462.

7 MATSUZAWA, H., ISHIBASHI, I. and KAWAMURA, M., Dynamic Soil and Water

Pressures of Submerged Soils, ASCE Journal of Geotechnical Engineering, Vol. 111,

No. 10, 1985, pp. 1161-1177.

8 WOOD, J.H. and ELMS, D.G., ‘Seismic Design of Bridge Abutments and Retaining

Walls’, RRU Bulletin 84, Vol. 2, Transit NZ, Wellington, 1990.

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APPENDIX J

LOAD COMBINATIONS

(Informative)

J1 GENERAL

This Appendix is aimed at assisting designers to determine the appropriate loading

combinations by reproducing those set out in AS 1170.1, AS 1170.2, and AS 1170.4, and

any other existing relevant loading specifications at the time of publication of this Standard

Italicized words reflect the requirement of AS 1170, not the requirements of this Standard.

The designer should determine whether such combinations are still valid at the time when

the design is to be carried out.

Other loads to be included with the basic combination given in AS 1170.1 for dead load

(including earth load), live load and earthquake load are hydrostatic pressure and loading

due to temperature movement.

NOTE: For the strength and stability limit state, this Standard requires the application of a load

factor of 1.25 on soil load and 1.0 on liquid pressure together with a reduction factor of between

0.95 and 0.75 on tan(φ) which is used to calculate the soil pressures. The combined effect of these

two factors is to give an effective load factor on active soil pressure in the range of 1.3 to 1.7 for

most common cases. This is consistent with AS 1170.1, which specifies load factors of 1.5 for

earth pressure and 1.25 on liquid pressure behind a structure.

J2 LOAD COMBINATIONS FOR STRENGTH LIMIT STATES

The loads for strength design have to be the most adverse combination of factored loads

that can reasonably coexist, factored from, but not limited to, the following combinations as

applicable:

(a) 1.25 G + 1.5 Q

(b) 1.25 G + Wu + ψcQ

(c) 1.25 G + 1.0 Feq + ψcQ

(d) 0.8 G + 1.5 Q

(e) 0.8 G + Wu

(f) 0.8 (G + ψcQ) + 1.0 Feq

Where G includes dead load of retained soil and ψc may be taken from AS 1170.1.

J3 LOAD COMBINATIONS FOR STABILITY LIMIT STATES

The structure has to be designed to prevent instability due to overturning, uplift and sliding,

as follows:

(a) The loads determined in accordance with Clause 4.1 have to be subdivided into

components tending to cause instability and components tending to resist stability.

(b) The design action effect (S*) has to be calculated from the components of the loads

tending to cause instability factored and combined in accordance with Clause 4.2.

(c) The design resistance effect (R*) has to be calculated from 0.8 times the part of the

dead load tending to resist the instability and the design capacity of the structural

components to resist instability (ΦR).

(d) The design resistance effect has to be greater than the design action effect.

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For the cases involving dead, live and earthquake loadings, the requirements may be

expressed by the following:

(i) 1.25 GC + 1.5 Q

C < 0.8G

R + (ΦR)

(ii) 1.25 GC + ψcQ

C + Wu

C < 0.8 G

R + (ΦR)

(iii) 1.25 GC + ψcQ

C + 1.0 F

Ceq <0.8 (G + ψcQ)

R + (ΦR)

where GC, Q

C, Wu

C and F

Ceq are parts of the dead, live, wind and earthquake loads that tend

to cause instability GR is the part of the load tending to resist instability and ΦR is the

design capacity of the structural component designed to resist instability (if any).

Examples of load components for limit states are given in Table J1.

The load cases A, B and C in Table J1 are as follows:

A Load case A—limit state load case for strength.

B Load case B—limit state load case for stability.

C Load case C—limit state load case for serviceability.

TABLE J1

EXAMPLES OF LOAD COMPONENTS FOR LIMIT STATES

(not including wind and earthquake loads)

Load case Load

factors Description

A B C

γg1 for γ1 Dead load (G1) of structure 1.25 0.8 1

γg2 for γ2 Dead load (G2) of fill behind structure 1.25 1.25 1

γg3 for γ3 Dead load (G3) of fill on structure 1.25 0.8 1

γg4 for γ4 Dead load of fill (G4) in front of structure 0.8 0.8 1

γgw for γw Weight of water behind or in front of structure 1 1 1

γq1 Traffic load (Q1) or other live load on structure 1.5 0 0.7(1) or 0.4(2) or 1.0(3)

γq2 Traffic load (Q2) or other live load behind

structure

1.5 1.5 0.7(1) or 0.4(2) or 1.0(3)

γq3 Traffic load (Q3) or other live load in front of

structure

0 0 0

NOTES:

1 Refers to short-term case.

2 Refers to short-term case.

3 Refers to storage load.

J4 LOAD COMBINATIONS FOR SERVICEABILITY LIMIT STATES

The design load for the serviceability limit states has to be taken from the factored loads for

short-term effects and long-term effects as follows:

(a) For short-term effects:

(i) Ws

(ii) ψs Q

(iii) G + Ws

(iv) G + ψs Q

(v) G + ψs Q + Ws

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(b) For long-term effects:

(i) G

(ii) ψl Q

(iii) G + ψl Q

ψs and ψl may be taken from AS 1170.1.

J5 EXAMPLE OF THE USE OF LOAD FACTORS

The elements of a gravity earth-retaining structure are illustrated in Figure J1. The effective

earth-retaining structure may include the structural system, its contained earth and any

superstructure (including overburden and supported structures) that acts integrally with the

structure. Examples of effective earth-retaining structures are illustrated in Figure J2.

The examples of the application of the load combinations for strength, stability and

serviceability limit states to the effective earth-retaining structure are illustrated in

Figure J3.

FIGURE J1 ELEMENTS OF A GRAVITY EARTH RETAINING STRUCTURE

J6 LOADING COMBINATIONS FOR SPECIAL STRUCTURES

In the calculation of traffic surcharge, the unfactored value has to be 20 kPa for roads of

functional road classes 1, 2, 3, 6 or 7 (see HB77). For all other functional class roads or

temporary roads (e.g. ramps) the unfactored traffic loading has to be 10 kPa.

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FIGURE J2 EFFECTIVE EARTH-RETAINING STRUCTURES

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FIGURE J3 LOAD COMBINATIONS

(not including wind and earthquake loads)

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J7 ASSESSMENT OF EARTH PRESSURES

J7.1 Earth and material pressures

J7.1.1 Load factors and pressures

The factored loads and resistances to be used in the design calculations (including earth

pressures, soil friction, soil bearing strength and component strengths) have to be those

corresponding to the most demanding combination of forces and material properties that

can reasonably coexist. For the most common cases such as strength, stability or

serviceability of gravity structures, this combination will result from the application of the

partial factors given in Sections 4 and 5.

NOTE: For serviceability, the partial load factors and partial material factors selected would

usually be equal to 1.0.

Where a more exigent design situation can reasonably be expected to result by using factors

that are different from those given in Sections 4 and 5, then they have to be considered. An

alternative set of partial load or material factors has to be considered so as not to diminish

the overall safety index of the structure or its components for strength, stability and

serviceability.

Having determined the factored loads and resistances that can reasonably be expected to

coexist in the most exigent situation, the structural load effects on the wall or reinforced

soil structure (i.e. bending moments, shears etc.) has to be calculated using equilibrium

principles without the application of further load factors.

Where the material to be retained consists substantially of weathered rock or rock-like

materials, then the principles of rock mechanics, including the assessment of any ‘wedge

type’ failures, have to be used in combination with the properties of backfill material to

assess the pressures on the wall or reinforced soil structure.

Information on earth pressures commonly used in the design of conventional retaining walls

and reinforced soil structures is given in Paragraph J7.2.

J7.1.2 Restraint conditions

As the earth pressure to be resisted by a wall or RSS structure is dependent on the

conditions of structural constraint, the designer has to give careful consideration to the

restraint conditions applying to the particular structure in the assessment of whether the

structure will be subjected to active, at rest, or passive earth pressures.

Whilst normally RSS structures are designed for a loading condition equivalent to the

‘active’ earth pressure condition, there are many situations under which a conventional

retaining wall structure can have ‘at rest’ or ‘passive’ loading conditions applied.

J7.1.3 Limit states

The designer has to give consideration to questions of overall slope stability, the possibility

of a general rotational failure of the soil mass and the bearing capacity of the foundation

strata in the determinations.

Information on the limit states commonly used in the design of conventional retaining walls

and RSS structures is given in Paragraph J7.2.

J7.2 Earth pressures

The earth pressure that acts on an earth-retaining structure is strongly dependent upon the

lateral deformations that can occur in the soil or weathered rock strata; thus, deformation

conditions should be estimated with reasonable accuracy as a part of the design process.

The minimum pressure that can be exerted against the wall is referred to as the ‘active’

condition and occurs when the wall moves sufficiently far outwards for the soil behind the

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Similarly, the maximum pressure that can be exerted against the wall is referred to as the

‘passive’ condition and occurs when the wall movement is towards the soil.

The amount of movement necessary to reach these failure conditions is dependent primarily

upon the type of materials behind the wall or RSS including the backfill material.

Some guidelines on these movements are given in Table J2.

For wall displacements less than those necessary to produce the failure conditions, it can be

assumed that the magnitude of the pressure upon the wall lies between the extreme values.

In weathered rock strata, the situation is more complex, requiring a consideration of the

principles of rock mechanics and how a pressure may be transmitted from the potential

failure wedge to the wall or RSS.

TABLE J2

WALL DISPLACEMENTS REQUIRED TO DEVELOP

ACTIVE AND PASSIVE EARTH PRESSURES (Ref. 1)

Soil State of stress Type of movement Necessary displacement

Active Parallel to wall 0.001 H

Active Rotation about base 0.001 H

Passive Parallel to wall 0.05 H

Sand

Passive Rotation about base > 0.10 H

Active Parallel to wall 0.004 H

Active Rotation about base 0.004 H

Clay

Passive — —

J8 INFLUENCE OF GEOMETRIC SHAPE OF RETAINING STRUCTURE

The geometric shape requirements of a retaining structure will vary depending on the

following:

(a) Level and slope of the retained ground surface and below the structure.

(b) Surcharge loadings.

(c) Soil properties in the select fill and general backfill zones.

(d) Bedrock levels and overall geological model assumed.

(e) Type of retaining structure, i.e. reinforced concrete wall, gravity type wall or

reinforced soil structure.

(f) Other considerations, e.g. areas of known seepage, soft ground areas or where future

excavation adjacent to retaining wall is planned.

For conventional gravity-retaining structures, an initial geometric sizing of base width (B)

equal to 0.7 times the height (H) is generally used to provide the required sliding and

overturning resistance and reduce foundation bearing pressures.

For reinforced soil structures, the geometry of the reinforced fill zone may be rectangular or

stepped (i.e. trapezoidal) in cross-section. Stepped wall geometries should only be used

where the founding conditions of the RSS are on stable rock strata. Figure J4 gives details

of minimum sizing of reinforced soil walls with various geometries to satisfy both internal

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J9 EARTH PRESSURES PRODUCED BY COMPACTION

Proper compaction of the backfill behind conventional retaining walls or within the select

fill zone of a reinforced soil structure is essential to ensure adequate shear strength and

stiffness. Whilst compaction is essential, its effect may induce large horizontal earth

pressures, which are subsequently ‘locked into’ the soil mass. These pressures can vary

both in magnitude and distribution and can exceed (Ref. 2) active earth pressures,

particularly in the upper part of the retaining structure.

A simplified method has been proposed by Ingold (Ref. 3) to estimate compaction-induced

earth pressures against retaining walls. The distribution of horizontal earth pressures is

idealized in Figure J5. Increased earth pressures given by phm are predicted to occur within

hc (depth below surface of the structure). For depths greater than hc a linear increase of

earth pressure with depth (either using Ka in the case of yielding structures or Ko in the case

of unyielding rigid structures) is assumed.

Compaction-induced horizontal stresses can sometimes be a significant contribution to the

total pressure against a retaining wall. In construction, it is good practice to place controls

on various construction equipment that are allowed to work behind such retaining

structures. In the case of a reinforced concrete structure with a thin cantilever stem, it is

advisable to use light compaction equipment such as vibratory plate compactors (say 125 kg

mass), which would induce compaction pressures of approximately 12 kPa.

A similar situation would apply in the compaction of select backfill in reinforced soil-

retaining structures where light compaction plant is used within 1.5 m behind the facings.

Heavier construction plant (e.g. 10.2 t static smooth wheel rollers) may induce horizontal

stresses up to 20 kPa and, therefore, such equipment should be used outside this zone. For

vibratory rollers, the combined effect of the roller dead weight and centrifugal force has to

be used in calculating the effective line loads Q1 imposed by the compaction plant.

J10 EFFECTS OF SURCHARGES

J10.1 Types of surcharges

Surcharges behind reinforced soil walls and retaining structures may be categorized into

two main types, as follows:

(a) Uniformly distributed loads — these may be continuous loads that act on the surface

of retained ground behind the structure, and include traffic loads and loadings from

materials stacked behind the retaining structure.

(b) Concentrated loads—these may be line loads (e.g. loadings from strip footings), point

loads (e.g. loads from isolated footings and piers) and area type loads, which have to

be considered in relation to the height and geometry of the wall.

Surcharges behind or on retaining structures may be of a permanent or temporary nature.

Examples of permanent loading are loads due to shallow foundations of an adjacent

structure or sill beam loadings of a bridge structure directly supported by reinforced soil

walls. Traffic-induced uniform loads for major roads may be classed as permanent.

Examples of temporary loads would be loads from construction plant or storage of goods or

construction materials that exert a transient load to the structure.

In some cases, the retaining structure may support other amenities such as sound barriers or

New Jersey kerbs that may attract loadings, e.g. wind loads or traffic impact loads. The

effect of such loads should be checked for the global and internal stability of the retaining

structure.

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J10.2 Design surcharge loads

The distribution of stresses on a retaining structure due to surcharge loads should be

carefully assessed in design. The design load factors are 1.5 for strength and stability limit

states, and 0.7 for the serviceability limit state. See Table J1 for examples of load

components for each limit state.

J10.3 Assessment of the effect of surcharge for conventional retaining structures

Each pressure induced by surcharge loads will depend on the load spreading properties of

the retained earth and the stiffness of the wall. Two approaches may be used to assess the

magnitude and distribution of lateral pressures induced by surcharge loading, as follows:

(a) Rankine active earth pressure theory—the trial wedge method and associated force

polygon methods may be employed (see Figure J6).

(b) Elasticity theory supported by experimental measurements—the earth pressure design

charts given by Terzaghi (Ref. 4) given in Figure J7 may be used to estimate lateral

pressure due to vertical line loads, point loads and horizontal line loads. These have

been modified from the Boussinesq (Ref. 5) solution for distribution of stresses in an

isotropic semi-infinite elastic medium based on experimental evidence.

Numerical modelling approaches (finite element analysis) may be used to assess the

magnitude and distribution of earth pressures for complex loaded retaining structures.

J10.4 Assessment of the effect of applied loadings on reinforced soil structures

For reinforced soil-retaining structures, the internal stresses are derived from two separate

load conditions, resulting from—

(a) the supporting function, and

(b) the retaining function.

These stresses should be superimposed for the determination of the total stresses due to

applied loadings and for the calculation of reinforcement stresses.

The supporting function requires the determination of the additional vertical and horizontal

stresses resulting from the diffusion of the applied loadings.

For vertical loadings, the distribution of vertical strip loadings through the fill may be

determined by a lateral dispersion defined by a slope of 2 vertically to 1 horizontally (see

Figure J8), or by calculating an appropriate stress distribution such as defined by

Boussinesq (Ref. 5). Vertical load dispersion has to take into account the effect of the face

on the available dispersion area.

For horizontal loadings, the distribution of horizontal strip loadings through the fill may be

determined by a vertical dispersion over the outside surface or facing of the structure

defined by a slope from the rear of the contact surface. The horizontal pressure distribution

on the outside surface or facing has to vary linearly from a maximum at the level of the

contact surface to zero at its lowest point (see Figure J8).

The retaining function takes into account the overall retaining structure loadings such as

self weight, superstructure and general surcharge loadings. These should then be taken in

combination with the overturning moments generated by the applied loads on the structure.

The diffusion of stresses imposed by applied loadings depends on the stiffness

characteristics of the structure. Further guidance on the selection and use of appropriate

design methods is provided in BS 8006.

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FIGURE J4 SIZING OF WALLS WITH VARIOUS GEOMETRIES A1

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LEGEND:

K = earth pressure coefficient (see Note 2)

Q1 = intensity of effective line load imposed by compaction plant (see Note 3)

zc,hc = critical depths as shown

γ = soil unit weight

Phm′ = maximum horizontal earth pressure induced by compaction

Ph′ = horizontal earth pressure induced by overburden stress

NOTES:

1 Figure based on Ingold (1979a and b).

2 For retaining walls that can move forward sufficiently to mobilize active condition in the fill, K = Ka. For unyielding

rigid structures, K = Ko. For walls supporting a fill slope, it may be assumed that the compaction-induced earth

pressure is the same as that given by the diagram above for a horizontal final surface, except zc should be taken as

zero.

3 For dead weight rollers, the effective line load is the weight of the roller divided by its roll width, and for vibratory

rollers it should be calculated using an equivalent weight equal to the dead weight of the roller plus the centrifugal

force generated by the roller’s vibrating mechanism. The centrifugal force may be taken to be equal to the dead

weight of the roller in the absence of trade data.

4 The compaction-induced earth pressure assumed in the design should be clearly stated on the drawings.

FIGURE J5 SIMPLIFIED METHOD FOR THE EVALUATION OF

COMPACTION-INDUCED EARTH PRESSURES

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FIGURE J6 TRIAL WEDGE METHOD OF ANALYSIS FOR SURCHARGE LOADING

BEHIND RETAINING STRUCTURES

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FIGURE J7 CALCULATION OF LATERAL PRESSURE ON A VERTICAL RETAINING

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FIGURE J8 APPLIED LOAD DISTRIBUTION IN REINFORCED SOIL STRUCTURES

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J11 EFFECTS OF WATER AND SEEPAGE

J11.1 General

Controlling hydrostatic pressures will often be the most important assumption in the design

of a retaining structure. None of the following is sufficient to ensure that hydrostatic

pressures will be adequately controlled throughout the design life of a structure:

(a) Providing a ‘drain’ on a cross-sectional drawing.

(b) Assuming or specifying that the backfill be ‘free draining’.

(c) Assuming that the wall itself is free draining.

If drains become ineffective, then the loads on a structure will increase substantially, and

the resistances will reduce substantially, such that the overall safety of the structure will be

halved.

J11.2 Uplift pressures

Hydrostatic pressures causing uplift on the base of retaining structures should be included

in design calculations unless positive means are adopted to ensure that they do not develop.

J11.3 Long-term conditions

Hydrostatic pressures behind and below a structure may be reduced by the design of an

appropriate drainage system. If such a system is incorporated in the design, then both the

construction and maintenance of the drainage system will need to be arranged to ensure that

the designer’s intent is met.

J12 REFERENCES

1 WU, T.H., Retaining Walls, Foundation Engineering Handbook, edited by Winterkon,

H.F. and Fang, H.Y., Van Nostrand Reinhold Co., New York, 1975.

2 RANKINE, W.J.M., On the stability of loose earth, Phil. Trans. Roy. Soc., London,

147, Part 1, 1857.

3 INGOLD, T.S., The effects of compaction on retaining walls, Wiley, New York

534 p.,1979.

4 TERZAGHI, K. and PECK, R.B., Soil Mechanics in Engineering Practice, 2nd

edition, Wiley, New York, 729 p., 1967.

5 BOUSSINESQ, J., Application des potentials a l’etude de l’equilibre et du

mouvement des solides elastiques. Gauthier-Villars, Paris, 1885.

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APPENDIX K

PARTIAL MATERIAL STRENGTH FACTOR DETERMINATION FOR SOIL

REINFORCEMENT

(Informative)

K1 GENERAL

This Appendix provides recommendations for the determination of material strength

reduction factors and uncertainty factors, which should be considered in the derivation of

long-term design strength of soil reinforcement, as defined in Section 5.

In the absence of internationally approved test method verified values, the appropriate

maximum material strength reduction factors defined in Paragraph K2, K3, K4 and K5

should be adopted.

K2 MANUFACTURING VARIATION FACTOR

The uncertainty factor (product), (Φup) may be determined from Table K1.

TABLE K1

UNCERTAINTY FACTOR (PRODUCT), (ΦΦΦΦup)

Situation ΦΦΦΦup

Rst is a guaranteed minimum 1.00

Rst is a characteristic value 0.95

K3 TIME-DEPENDENT STRESS/STRAIN BEHAVIOUR FACTORS

Allowable design load of the reinforcement should be based on real time creep tests for a

period not less than 10% of the design life. For design lives greater than 10 years, the

allowable design load of the reinforcement should be based on a minimum duration of

104 hours.

Extrapolation of two log cycles is permitted provided the extrapolation is based on

supported test data derived from real time or accelerated tests, such as those carried out at a

range of temperatures.

The reduction factors for the extrapolation in Table K2 should be used.

In the absence of appropriate test results the reduction factors φrc in Table K3 should be

used.

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TABLE K2

UNCERTAINTY FACTOR (EXTRAPOLATION), (ΦΦΦΦue)

ΦΦΦΦue

Log cycles of extrapolation Material

0 1 1.5 2

Metals 1.00 1.00 1.00 1.00

Polyester 1.00 1.00 0.88 0.75

Polyethylene 1.00 1.00 0.88 0.75

Polypropylene 1.00 1.00 0.88 0.75

TABLE K3

REDUCTION FACTOR (CREEP), (ΦΦΦΦrc)

Material Service life

(years) ΦΦΦΦrc

All metals 100 1.00

Polyester 30

100

0.60

0.50

Polyethylene 30

100

0.33

0.30

Polypropylene 30

100

0.20

0.17

K4 CONSTRUCTION DAMAGE FACTOR

The reduction factor (construction or installation) (Φri) should be determined by reference

to the material and the structure of the product, as well as the nature of the backfill and the

compactive effort and should be determined from actual tests undertaken in controlled

conditions. In the absence of such test results, the values in Table K4 should be used.

TABLE K4

REDUCTION FACTOR (CONSTRUCTION OR INSTALLATION) (ΦΦΦΦri)

Situation ΦΦΦΦri

Steel of minimum thickness 4 mm in all backfills 1.00

Geosynthetic material in fine sand 0.90 – 0.8

Geosynthetic material in coarse gravel 0.90 – 0.6

NOTE: Some polyester grids in coarse gravel will suffer damage greater than 40%, thus requiring

reduction factors less than 0.6.

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K5 ENVIRONMENTAL FACTORS

K5.1 General

The environmental degradation factors that cover chemical and biological attack of the

reinforcement material are the following:

(a) Reduction factor (thickness), Φrt

(b) Reduction factor (strength), Φrs

(c) Reduction factor (temperature), Φrst

(d) Uncertainty factor (degradation), Φud

K5.2 The reduction factor (thickness), ΦΦΦΦrt

The reduction factor (thickness), (Φrt) takes into account the loss of material with time, as

follows:

Φrt = (1 − ∆A/Ao) . . . K5(1)

where

∆A = loss of section area

Ao = original section area

For steel reinforcements, loss of section area should be estimated from the following

equation:

∆A = 2Actn . . . K5(2)

where

Ac = corrosion loss at t = 1 year

t = time in years

n = constant representing rate of change of corrosion rate

The maximum loss of section area over the design life of the structure should be

0.33 × original section area.

K5.3 The reduction factor (strength), (ΦΦΦΦrs)

The reduction factor (strength), Φrs, takes into account the alteration of the material itself

and the variability or unevenness of the corrosion or degradation and is related to the

reduction factor (thickness) as follows:

ΦrtΦrs = 1 − K(1 − Φrt) . . . K5(3)

where

K is given by the equation

∆T/To = K(∆A/Ao) . . . K5(4)

and

∆T = loss of tensile strength

To = original tensile strength

For steel, minimum values of K may be taken as follows:

K = 1.5 for galvanized steel in standard environments

= 2.0 for black steel in standard environments

= 2.5 for black steel in aggressive environments

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K5.4 Steel reinforcement

For steel reinforcement, a combined reduction factor (thickness and strength loss), Φrt Φrs

may be estimated from the corrosion allowance as per Table K5 (flat strip) and Table K6

(round bar). The corrosion allowance for steel reinforcements is dependent on the properties

of the backfill and the environment for a given service life and should be estimated from

Appendix J.

NOTE: Corrosion allowance is given by the relevant authorities and takes into account the K

values of the base materials.

K5.5 Polymer reinforcement

For polymer reinforcements, the reduction factor (thickness) (Φrt), and the reduction factor

(strength) Φrs, will be in the following ranges:

(a) Reduction factor (thickness) (Φrt) ........................................................... 0.90 to 1.00.

(b) Reduction factor (strength) (Φrs)............................................................. 0.50 to 0.90.

K5.6 The reduction factor (temperatures) (ΦΦΦΦrst)

The reduction factor (temperature) should be obtained from manufacturers of the

reinforcement and should account for projected temperatures at the depth of placement.

K5.7 The uncertainty factor (degradation) (ΦΦΦΦud)

The uncertainty factor (degradation) may be taken as 0.8 for all materials.

TABLE K5

COMBINED REDUCTION FACTOR (ΦΦΦΦrt ΦΦΦΦrs)

FOR FLAT STEEL STRIP

ΦΦΦΦrt ΦΦΦΦrs

Corrosion allowance (mm) Original thickness

(mm)

0.5 1.0 1.5 2.0

4 0.87 0.75 0.62 0.50

5 0.90 0.80 0.70 0.60

6 0.92 0.83 0.75 0.67

TABLE K6

COMBINED REDUCTION FACTOR (ΦΦΦΦrt ΦΦΦΦrs)

FOR ROUND STEEL BAR

ΦΦΦΦrt ΦΦΦΦrs

Corrosion allowance (mm) Original diameter

(mm)

0.5 1.0 1.5 2.0

8 0.88 0.77 0.66 0.56

9 0.89 0.79 0.69 0.60

10 0.90 0.81 0.72 0.67

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AMENDMENT CONTROL SHEET

AS 4678—2002

Amendment No. 1 (2003)

REVISED TEXT

SUMMARY: This Amendment applies to the Clauses 1.1, 1.2.2, 1.4.1.22 (new), 1.4.1.23 (new), 1.4.1.24 (new),

1.4.1.25 (new), 1.5, 4.1, 4.2, 5.5.1.2, 5.5.1.3, 5.5.1.4, 5.5.1.6, 5.5.2.2, 5.5.3 and 7, Tables 1.1, 2.1, 4.1, 5.1(A),

5.1(B), 5.2, 5.3, 7.1, A1 (new), A2 (new), B1, E1, I3, K3 and K6, Figures 1.2 (new), 3.1(E), A1, E2, J2, J4, J5

and J6, Paragraphs A3 (new), B4.2.4, E2.3, H2, H3, I5, I14, I15, J2, J3, K5.2 and K5.3.

Published on 7 July 2003.

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AS 4678—2002

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AS 4678—2002

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Standards Australia

Standards Australia is an independent company, limited by guarantee, which prepares and publishes

most of the voluntary technical and commercial standards used in Australia. These standards are

developed through an open process of consultation and consensus, in which all interested parties are

invited to participate. Through a Memorandum of Understanding with the Commonwealth government,

Standards Australia is recognized as Australia’s peak national standards body.

Australian Standards

Australian Standards are prepared by committees of experts from industry, governments, consumers

and other relevant sectors. The requirements or recommendations contained in published Standards are

a consensus of the views of representative interests and also take account of comments received from

other sources. They reflect the latest scientific and industry experience. Australian Standards are kept

under continuous review after publication and are updated regularly to take account of changing

technology.

International Involvement

Standards Australia is responsible for ensuring that the Australian viewpoint is considered in the

formulation of international Standards and that the latest international experience is incorporated in

national Standards. This role is vital in assisting local industry to compete in international markets.

Standards Australia represents Australia at both ISO (The International Organization

for Standardization) and the International Electrotechnical Commission (IEC).

Electronic Standards

All Australian Standards are available in electronic editions, either downloaded individually from our Web

site, or via on-line and CD ROM subscription services. For more information phone 1300 65 46 46 or

visit us at

www.standards.com.au

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GPO Box 5420 Sydney NSW 2001

Administration Phone (02) 8206 6000 Fax (02) 8206 6001 Email [email protected]

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Internet www.standards.com.au

ISBN 0 7337 4238 6 Printed in Australia

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Documents

As 4678-2002 Earth-Retaining Structures